[BUGFIX] #5085 Allow first_name and last_name in the registration form

Change-Id: I8dcfd8be36b1e5aec70e4fb67a8f13d880fbb9f2
Reviewed-on: http://review.typo3.org/32533
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>