Allow gitweb to be configured to show refs out of refs/heads/ as if
they were branches.
* kn/gitweb-extra-branch-refs:
gitweb: Denote non-heads, non-remotes branches
gitweb: Add a feature for adding more branch refs
gitweb: Return 1 on validation success instead of passed input
gitweb: Move check-ref-format code into separate function