Username max_length does not match email max_length

This means that emails get truncated when creating usernames, if the email address is > 30 chars.

I'm not sure this is the "right" change, but it's certainly the smallest.
* Small Django tweak to make usernames 75 chars long.  
* In order to work with old installationa and new installations, generated a django.contrib.auth schema change, but put it under the registration folder.

This is to resolve issue #123