mingw32-git: Improve wording in a comment a bit

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
mingw32-git: Package git-subtree into "ext"

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
mingw32-git: Package git-contacts into "ext"

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
mingw32-git: Remove the deprecated version 1.8.3

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>