0.8dev: Translatable message was generating a `gettext` error. Refs #639.

Patch by Olemis.msg = _("Missing ticket field '%(field)s'.", field='product') 


git-svn-id: https://svn.apache.org/repos/asf/bloodhound/trunk@1518010 13f79535-47bb-0310-9956-ffa450edef68