Fixes to support Python 2.6 again.

Details:

- Added Python 2.6 again to .travis.yml (it was removed in commit 4486bcb).

- Replaced the use of dictionary comprehensions in `git/cmd.py` around
  line 800 with the code before that change (in commit 25a2ebf).
  Reason: dict comprehensions were introduced only in Python 2.7.

- Changed the import source for `SkipTest` and `skipIf` from `unittest.case`
  to first trying `unittest` and upon ImportError from `unittest2`.
  This was done in `git/util.py` and in several testcases.
  Reason: `SkipTest` and `skipIf` were introduced to unittest only
  in Python 2.7, and `unittest2` is a backport of `unittest` additions
  to Python 2.6.

- In git/test/lib/helper.py, fixed the definition of `assertRaisesRegex`
  to work on py26.

- For Python 2.6, added the `unittest2` dependency to `requirements.txt`
  and changed `.travis.yml` to install `unittest2`. Because git/util.py
  uses SkipTest from unittest/unittest2, the dependency could not be added
  to `test-requirements.txt`.

- Fixed an assertion in `git/test/test_index.py` to also allow
  a Python 2.6 specific exception message.

- In `is_cygwin_git()` in `git/util.py`, replaced `check_output()` with
  `Popen()`. It was added in Python 2.7.

- Enabled Python 2.6 for Windows:

  - Added Python 2.6 for MINGW in .appveyor.yml.

  - When defining `PROC_CREATIONFLAGS` in `git/cmd.py`, made use of certain
    win32 and subprocess flags that were introduced in Python 2.7, dependent
    on whether we run on Python 2.7 or higher.

  - In `AutoInterrupt.__del__()` in `git/cmd.py`, allowed for `os` not having
    `kill()`. `os.kill()` was added for Windows in Python 2.7 (For Linux, it
    existed in Python 2.6 already).

9 files changed, 48 insertions, 17 deletions

diff --git a/git/test/lib/helper.py b/git/test/lib/helper.py
index 1515f2a1..743f720c 100644
--- a/git/test/lib/helper.py
+++ b/git/test/lib/helper.py
@@ -7,20 +7,24 @@ from __future__ import print_function
 
 import contextlib
 from functools import wraps
+import sys
 import io
 import logging
 import os
 import tempfile
 import textwrap
 import time
-from unittest import TestCase
-import unittest
 
-from git.compat import string_types, is_win, PY3
+from git.compat import string_types, is_win
 from git.util import rmtree, cwd
 
 import os.path as osp
+if sys.version_info[0:2] == (2, 6):
+    import unittest2 as unittest
+else:
+    import unittest
 
+TestCase = unittest.TestCase
 
 ospd = osp.dirname
 
@@ -335,8 +339,11 @@ class TestBase(TestCase):
       of the project history ( to assure tests don't fail for others ).
     """
 
-    if not PY3:
-        assertRaisesRegex = unittest.TestCase.assertRaisesRegexp
+    # On py26, unittest2 has assertRaisesRegex
+    # On py3, unittest has assertRaisesRegex
+    # On py27, we use unittest, which names it differently:
+    if sys.version_info[0:2] == (2, 7):
+        assertRaisesRegex = TestCase.assertRaisesRegexp
 
     def _small_repo_url(self):
         """:return" a path to a small, clonable repository"""
diff --git a/git/test/test_base.py b/git/test/test_base.py
index cec40de8..69f161be 100644
--- a/git/test/test_base.py
+++ b/git/test/test_base.py
@@ -7,7 +7,10 @@
 import os
 import sys
 import tempfile
-from unittest import skipIf
+try:
+    from unittest import SkipTest, skipIf
+except ImportError:
+    from unittest2 import SkipTest, skipIf
 
 from git import (
     Blob,
@@ -131,7 +134,6 @@ class TestBase(TestBase):
         try:
             file_path.encode(sys.getfilesystemencoding())
         except UnicodeEncodeError:
-            from unittest import SkipTest
             raise SkipTest("Environment doesn't support unicode filenames")
 
         with open(file_path, "wb") as fp:
diff --git a/git/test/test_fun.py b/git/test/test_fun.py
index 9d436653..b472fe19 100644
--- a/git/test/test_fun.py
+++ b/git/test/test_fun.py
@@ -1,6 +1,9 @@
 from io import BytesIO
 from stat import S_IFDIR, S_IFREG, S_IFLNK
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git.compat import PY3
 from git.index import IndexFile
diff --git a/git/test/test_index.py b/git/test/test_index.py
index 1abe22f4..071ac623 100644
--- a/git/test/test_index.py
+++ b/git/test/test_index.py
@@ -13,7 +13,10 @@ from stat import (
 )
 import sys
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     IndexFile,
@@ -149,8 +152,9 @@ class TestIndex(TestBase):
         except Exception as ex:
             msg_py3 = "required argument is not an integer"
             msg_py2 = "cannot convert argument to integer"
-            ## msg_py26 ="unsupported operand type(s) for &: 'str' and 'long'"
-            assert msg_py2 in str(ex) or msg_py3 in str(ex), str(ex)
+            msg_py26 = "unsupported operand type(s) for &: 'str' and 'long'"
+            assert msg_py2 in str(ex) or msg_py3 in str(ex) or \
+                msg_py26 in str(ex), str(ex)
 
         ## 2nd time should not fail due to stray lock file
         try:
diff --git a/git/test/test_remote.py b/git/test/test_remote.py
index 8b50ea35..aae4fb9f 100644
--- a/git/test/test_remote.py
+++ b/git/test/test_remote.py
@@ -6,7 +6,10 @@
 
 import random
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     RemoteProgress,
diff --git a/git/test/test_repo.py b/git/test/test_repo.py
index 374a26ee..9ad80ee6 100644
--- a/git/test/test_repo.py
+++ b/git/test/test_repo.py
@@ -11,7 +11,10 @@ import os
 import pickle
 import sys
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf, SkipTest
+except ImportError:
+    from unittest2 import skipIf, SkipTest
 
 from git import (
     InvalidGitRepositoryError,
@@ -53,7 +56,6 @@ from git.test.lib import (
 from git.util import HIDE_WINDOWS_KNOWN_ERRORS, cygpath
 from git.test.lib import with_rw_directory
 from git.util import join_path_native, rmtree, rmfile, bin_to_hex
-from unittest import SkipTest
 
 import functools as fnt
 import os.path as osp
diff --git a/git/test/test_submodule.py b/git/test/test_submodule.py
index 7b05f49a..59a40fa0 100644
--- a/git/test/test_submodule.py
+++ b/git/test/test_submodule.py
@@ -3,7 +3,10 @@
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 import os
 import sys
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 import git
 from git.cmd import Git
diff --git a/git/test/test_tree.py b/git/test/test_tree.py
index f9259874..ab85bc9c 100644
--- a/git/test/test_tree.py
+++ b/git/test/test_tree.py
@@ -6,7 +6,10 @@
 
 from io import BytesIO
 import sys
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     Tree,
diff --git a/git/test/test_util.py b/git/test/test_util.py
index 8f8d2272..525c8609 100644
--- a/git/test/test_util.py
+++ b/git/test/test_util.py
@@ -6,7 +6,11 @@
 
 import tempfile
 import time
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
+
 
 import ddt