Fix buttons on the ipad, enabling the maze and puzzle apps to work correctly.

We do this by calling the onclick handler in response to the ontouchend event.

R=neil.fraser@gmail.com

Review URL: https://codereview.appspot.com/9849049

git-svn-id: http://blockly.googlecode.com/svn/trunk@1073 c400ca83-b69d-9dd7-9705-49c6b8615e23