Add git submodule support (to detect submodule repos)

[varunsairam]

Found that git submodules were not getting detected by vcs. Believe the issue comes down to file structure and type.

(Also faced in issue: #198)

Typical git repo

git_repo
    |--- .git (directory)

Submodule repo

outer_repo
    |--- .git (directory)
    |--- submodule_repo
         |--- .git (file)

Contents of .git file (the one inside the submodule_repo):

gitdir: ../.git/modules/submodule_repo

So effectively, submodules don't have .git directory of their own but rather a .git linked file that links to the directory in the outer .git directory.

Currently, it appears that vcstool is designed to determine if a repo is a git repo by checking for only a .git directory:

vcstool/vcstool/clients/git.py

Line 31 in daf3893

return os.path.isdir(os.path.join(path, '.git'))

Tried to fix this here. The submodules now seem to get detected as git repos. Hope there would be no unintended consequences though?

[rty813]

really need this feature!!!