vcsh: Initialize repos with --shared=0600

Configurations and other dotdir content may be highly confidential.

Ensure we're not leaking/exposing information by making vcsh
repositories user-accessible, only.

Thanks to Enrico Zini for realizing this was a problem.
vcsh: Pass along exit code

If `git foo` exits 13, it would be prudent for vcsh to exit 13, as well.
Start with support for `vcsh pull`.
vcsh: Fix up the rest of the (relevant) git calls
Merge branch 'feature/chown'