Fix bug 1110863 - Commit the db transaction before completing signup.

This is a regression from bug 1104864 and relateds to the abysymal
behavior of the Django 1.4 transaction middleware. Celery is just a
pawn in its game. God damnit.
Merge pull request #2950 from jezdez/bug1110863

Fix bug 1110863 - Commit the db transaction before completing signup.