Got rid of autocomplete for user referral box.

It was snazzy, but it required a list of all the users in the
system to be loaded with the page, which, as you might expect,
made the page take *really* long to load.
Fix a problem with the last commit.

Now it allows you to leave the "referred by" field blank.
Merge pull request #17 from djpetti/devel

Fix slow page loading.