Fix PageUserAdmin for custom user model.

Don't crash at startup if the custom user model has no first_name and
last_name fields.

The PageUserAdmin still won't actually work, so you'll have to subclass
it and change the fieldsets to include the fields that actually work, but
at least you can import it now.
Modify the custom user model to have fewer fields.

Allows us to test whether PageUserAdmin works or not.
Fix tests throwing another exception during teardown.

This conceals the original error that you actually want to fix.
Test against custom user model to trigger failures.
first lines for MP
Merge commit '2eb9e84' into fix_custom_user_model_admin

Conflicts:
	.travis.yml
first tests passing
removed some more mptt stuff
reducing the test failures... how could have mptt ever have functioned?
fixed a lot of tests again
and other test fixed
Merge branch 'develop' into treebeard
fixed all non query number related tests
fixed more bugs
fixed all tests \o/
deleted some leftover templates
removed some print statements
migration from between
Merge branch 'develop' into treebeard
fixed some reversion bugs