drupalmu_helper_context doesn't detect comment editing

Issue Summary

If you edit a comment to a blog that you've previously submitted, you should get the same theme as you did when first creating the comment using reply. However, the drupalmu_helper_context function doesn't detect this case.

This is non-trivial to fix, because the path only contains the cid, unlike the reply case. For Drupal 6, I believe the simplest approach is to call _comment_load on the cid to get the nid, then load the node to get the uid. For Drupal 7, it may be best to wait to see how comments evolve.