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).

1 files changed, 7 insertions, 3 deletions

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: