vcs: add missing parameters to base class method.

rhodecode/lib/vcs/backends/base.py

@@ -421,7 +421,7 b' class BaseRepository(object):'
 
     def _merge_repo(self, shadow_repository_path, target_ref,
                     source_repo, source_ref, merge_message,
-                    merger_name, merger_email, dry_run=False):
+                    merger_name, merger_email, dry_run=False, use_rebase=False):
         """Internal implementation of merge."""
         raise NotImplementedError