Projects/Gitolite: Make the default branch the real default.

Created by: Olipro

Gitlab will now tell gitolite to update the HEAD pointer over ssh using the symbolic-ref command - this ensures that when performing a git clone, the branch you receive if none is specified will actually be the one you configured as default.

This also resolves breakage when your repo lacks any branch named "master.

Depends on gitlabhq/gitolite#4