Fix UrlInsteadOf to handle multiple strings

For complex .gitconfig url rewrites, multiple insteadOf lines may be
used for a url. Search all of them for the right rewrite.

Change-Id: If5e9ecd054e86226924b0baf513801cd57c389cd

git_config.py

@@ -217,9 +217,9 @@ class GitConfig(object):
     """Resolve any url.*.insteadof references.
     """
     for new_url in self.GetSubSections('url'):
-      old_url = self.GetString('url.%s.insteadof' % new_url)
-      if old_url is not None and url.startswith(old_url):
-        return new_url + url[len(old_url):]
+      for old_url in self.GetString('url.%s.insteadof' % new_url, True):
+        if old_url is not None and url.startswith(old_url):
+          return new_url + url[len(old_url):]
     return url
 
   @property