This removes the one-off GIT_CDECL and adds a new standard way of
doing this named GIT_STDLIB_CALL with a src/win32 specific def
when on the Windows platform.
There were quite a few places were spaces were being used instead of
tabs. Try to catch them all. This should hopefully not break anything.
Except for `git blame`. Oh well.
1. The license header is technically not valid if it doesn't have a
copyright signature.
2. The COPYING file has been updated with the different licenses used in
the project.
3. The full GPLv2 header in each file annoys me.
