This protects against `.split(None)` which uses consecutive whitespace
as a separator to overlook paths where a single space is the filename.
For example, in this diff line:

line = ':100644 000000 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
0000000000000000000000000000000000000000 D       '

The deleted file is a file named ' ' (just one space).  It's entirely
possible to commit this, remove, and to produce the following output
from `git diff`:

git diff --name-status <SHA1> <SHA2>
D
M       path/to/another/file.py
...

This would cause the initial `.split(None, 5)` to fail as it will count
all consecutive whitespace as a separator, disregarding the ' ' (single
space)  filename.

Git utilizes multiple environment variables to control various
behaviours. Make sure to set LC_MESSAGES on a copy of the environment
instead of discarding any variables that may be set by the user or
default shell environment such as EDITOR.

Add test to assert that when overriding GIT_EDITOR via os.environ that
the modified value will be picked up by and git commands called.

Adjusted patch to only run git command in shell mode on windows.
Conflicts:
	git/cmd.py

Backport of https://github.com/gitpython-developers/GitPython/pull/131

This includes a few fixes to not break backwards compatiblity