Force reloading Git DB cache on error

Just recreating the object does not help as gitdb module is holding
cache of objects and won't reread it unless explicitely told so.

This still leaves open question how to detect these situations better.

Fixes #449
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/subproject.py

@@ -377,16 +377,6 @@ class SubProject(models.Model, PercentMixin, URLMixin, PathMixin):
             self._linked_subproject = SubProject.objects.get_linked(self.repo)
         return self._linked_subproject
 
-    def reset_git_repo(self):
-        '''
-        Resets git repository object database.
-        '''
-        if self.is_repo_link:
-            self.linked_subproject.reset_git_repo()
-            return
-
-        self._git_repo = None
-
     @property
     def git_repo(self):
         '''
@@ -414,7 +404,7 @@ class SubProject(models.Model, PercentMixin, URLMixin, PathMixin):
         except ODBError:
             # Try to reread git database in case our in memory object is not
             # up to date with it.
-            self.reset_git_repo()
+            self.git_repo.odb.update_cache()
             return self.git_repo.commit('origin/%s' % self.branch)
 
     def get_repo_url(self):