Properly try to update repo before doing merge

Issue #511
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/vcs.py

@@ -640,6 +640,11 @@ class HgRepository(Repository):
         if abort:
             self.execute(['update', '--clean', '.'])
         else:
+            try:
+                # First try update
+                self.execute(['update'])
+            except RepositoryException as error:
+                # Fallback to merge
                 try:
                     self.execute(['merge', '--tool', 'internal:merge'])
                 except RepositoryException as error:
@@ -719,7 +724,7 @@ class HgRepository(Repository):
         (is missing some revisions).
         """
         missing_revs = self.execute(
-            ['log', '--branch', 'tip', '--prune', 'default']
+            ['log', '--branch', 'tip', '--prune', '.']
         )
         return missing_revs != ''