Revert to SHA1 hashing for stored passwords

This is required for the old style community auth system that is still
in use by the commitfest app. Once that has been retired or upgraded,
this patch should be reverted.

Existing passwords are automatically converted once the user logs in to
the main website once.
Fix creation of new objects with notifications that have ManyToMany relationships

This broke in django 1.4 since it fires based on the contents of an error message,
and the message changed. Most visible due to the fact that it completely broke
creation of new organsation objects.