Fix validation bug with non-required radio buttons

jquerytools 1.2.7 introduced a new "bug" (jquerytools issue 733) where radio buttons whose required attribute is false are still required by the validator.  This causes a validation error, "please select an option", during validation which used to work.

There was much debate on the issue ticket for jquerytools and it appears to have been merged into master.  Thus, this patch backports a bugfix which will be in the next jquerytools release.