Git Support ready-ness

[David Nolden]

I think we don't have the ressources to maintain a git plugin that
works with many versions, so we should simply go the version-check way
(it could be checked when kdevelop decides whether a directory is
controlled by git, it could always return false and do a warning on
the command-line if the version is too old). Personally I can solve
this for myself by doing a _local_ installation of a current git
version.

Greetings, David