Make detecting bare Git repositories more robust

Git remote repositories may end on '.git', e.g. myrepo.git. Just checking
for a repository path to end on '.git' causes 'Repository not found' errors
in such a case. To distinguish between bare and normal Git repositories,
check if there is a '/.git' part at the end of the repository path
(i.e. if GIT_DIR is pointing to '.' (bare) or '.git').