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, 9 insertions, 5 deletions

diff --git a/git/cmd.py b/git/cmd.py
index 72ba82c3..78b5ff70 100644
--- a/git/cmd.py
+++ b/git/cmd.py
@@ -139,9 +139,9 @@ def dict_to_slots_and__excluded_are_none(self, d, excluded=()):
 CREATE_NO_WINDOW = 0x08000000
 
 ## CREATE_NEW_PROCESS_GROUP is needed to allow killing it afterwards,
-# seehttps://docs.python.org/3/library/subprocess.html#subprocess.Popen.send_signal
+# see https://docs.python.org/3/library/subprocess.html#subprocess.Popen.send_signal
 PROC_CREATIONFLAGS = (CREATE_NO_WINDOW | subprocess.CREATE_NEW_PROCESS_GROUP
-                      if is_win
+                      if is_win and sys.version_info >= (2, 7)
                       else 0)
 
 
@@ -245,7 +245,7 @@ class Git(LazyMixin):
                 return
 
             # can be that nothing really exists anymore ...
-            if os is None or os.kill is None:
+            if os is None or getattr(os, 'kill', None) is None:
                 return
 
             # try to kill it
@@ -831,8 +831,12 @@ class Git(LazyMixin):
         :return: Same as ``execute``"""
         # Handle optional arguments prior to calling transform_kwargs
         # otherwise these'll end up in args, which is bad.
-        _kwargs = {k: v for k, v in kwargs.items() if k in execute_kwargs}
-        kwargs = {k: v for k, v in kwargs.items() if k not in execute_kwargs}
+        _kwargs = dict()
+        for kwarg in execute_kwargs:
+            try:
+                _kwargs[kwarg] = kwargs.pop(kwarg)
+            except KeyError:
+                pass
 
         insert_after_this_arg = kwargs.pop('insert_kwargs_after', None)