Preg type started as a fork from shortanswer which isn't good.

Following the work done in MDL-17229 (thank's, Tim) preg question type can now be inherited from shortanswer type. This eliminate (almost all) code duplication between question types, makes preg qtype much shorter and allows it to automatically accept all fixes and improvments in shortanswer question.

The updated question will only work with Moodle 1.9.5 or later (actually 1.9.4.+ starting from March 2009)