protected_branch.rb

1. The `open_branches` method is used to provide a list of branches
   while creating a protected branch.

2. It makes sense to include branches which are matched by one or more
   wildcard protected branches, since the user might want to make exact
   protected branches from these as well.

3. This also provides a large performance improvement. On my machine, in
   a project with 5000 branches and 2000 protected branches, the
   `ProtectedBranches#index` page went from a 40 seconds load time to 4
   seconds (10x speedup).