Improve git repository setup

With configured origin remote in global git config, current approach
failed as it had half existing remote (repo.remotes.origin did not
exist, but git remote did show it).

Now we do not try to add origin if git already sees it and we configure
branches to fetch, this should also prevent fetching of branches we
don't follow.

Fixes #268.

trans/models/subproject.py

@@ -394,22 +394,32 @@ class SubProject(models.Model, PercentMixin, URLMixin):
         '''
         if self.is_repo_link():
             return self.linked_subproject.configure_repo(validate)
-        # Get/Create origin remote
-        try:
-            origin = self.git_repo.remotes.origin
-        except AttributeError:
+
+        # Create origin remote if it does not exist
+        if 'origin' not in self.git_repo.git.remote().split():
             self.git_repo.git.remote('add', 'origin', self.repo)
-            origin = self.git_repo.remotes.origin
-        # Check remote source
-        if origin.url != self.repo:
-            self.git_repo.git.remote('set-url', 'origin', self.repo)
+
+        # Set remote URL
+        self.git_repo.git.remote('set-url', 'origin', self.repo)
+
+        # Set branch to track
+        # We first need to add one to ensure there is at least one branch
+        self.git_repo.git.remote('set-branches', '--add', 'origin', self.branch)
+        # Then we can set to track just one
+        self.git_repo.git.remote('set-branches', 'origin', self.branch)
+
+        # Get object for remote
+        origin = self.git_repo.remotes.origin
+
         # Check push url
         try:
             pushurl = origin.pushurl
         except AttributeError:
             pushurl = ''
+
         if pushurl != self.push:
             self.git_repo.git.remote('set-url', 'origin', '--push', self.push)
+
         # Update
         self.update_remote_branch(validate)