This is follow-up for 56c66ee486 allowing admin
to see private repositories, even when not being member of them.

This allows the admin to disable the version information about gogs and
go in use in the footer.

This makes Gogs repos work with godoc.org: https://github.com/golang/gddo/wiki/Source-Code-Links

- prevent create reop on existed path

This is because git command line shows the failure reason only if Content-Type is text/plain.