Patch to integrate with ubercart checkout form

This patch adds the originality check to the username field on the ubercart checkout form

Right now it only works properly when the checking mode is set to auto. For it to work in manual, the username_check_manual.js file needs to be edited so a context is set for both #username-check-button (default register form) and #edit-panes-customer-new-account-username-check-button (the ubercart checkout). Ill probably get around to it eventually, but if anyone with js skills gets there first, that would be great