Support attaching comments to cases using mailhandler.module

Currently, if you try to attach a comment to a casetracker_basic_case using http://drupal.org/project/mailhandler, the case's state data is reset (values of fields type, priority, status, assigned_to are all nullified).

The attached patch injects the casetracker data into mailhandler.module's synthetically-generated comments, so that cases maintain their current state data.