2.4 wordwrap unicode aware

Solves https://cakephp.lighthouseapp.com/projects/42648/tickets/3981-stringwrap-is-not-unicode-aware
Not sure if that is the cleanest solution, though..

The only other place where the plain wordwrap() method is still used is the CakeEmail class:

     explode("\n", wordwrap($line, $wrapLength, "\n", $cut))

But I think this is fine as it is just the splitting into the required max length (this does not need to be this exact). IMO performance outweights accuracy here.