Add support for git fsck

[yogeshjain999]

There is no method present to check for dangling and invalid objects in repository.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[don-reba]

I really wish this were supported.

[jcouball]

@don-reba I'll look into this one.

[jcouball]

@don-reba does #885 give you what you need?