Prevent authorized user from opening register page

There is an odd check of http method.
When authorized user opens the registration page he should be redirected out of it immediately because his next actions would be obviously in vain (based on code) but user himself cannot be sure of its result... will the new user be actually created or won't, and even will form be submitted or won't.
Merge pull request #394 from Dropaq/patch-1

Prevent authorized user from opening register page