Bug #5972 - Some question types mark a blank answer inconsistently.

Bug #5972 - Some question types mark a blank answer inconsistently.

Also, cleaned up the marking code for numerical and short answer questions, partly by making the base-class method more useful.

Rewrote the way the way short answer questions do wildcard matching to be more robust, Unicode safe, and generally not suck.

This is a big change, so I am pleased to report I tested it using my new Selinium  test suite. See: http://moodle.org/mod/forum/discuss.php?d=51161