minimum version support for git init and git clone

git init can be run in the target directory as far back as 1.5.0.rc1,
so the temporary directory is created first, and git init is run from within

git clone can clone into an already existing directory only since 1.6.2.rc0,
so since the target directory is created by File::Temp, we can't support
git clone in ealier versions
test_repository only supports clone for git >= 1.6.2.rc0