scm: mercurial: temporary disable tags and branches at model (#1981, #7246, #4455).

Until latest_changesets supports tags and branches.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4871 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/repository/mercurial.rb

@@ -44,6 +44,14 @@ class Repository::Mercurial < Repository
     changeset.scmid
   end
 
+  def branches
+    nil
+  end
+
+  def tags
+    nil
+  end
+
   def diff_format_revisions(cs, cs_to, sep=':')
     super(cs, cs_to, ' ')
   end