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).