sproutcore/sproutcore — pull request #920 by fairbanksg (2013-02-07 20:51:48+00:00)
Title: Allow SC.State's to disallow a state transition.

Added a stateCanBecomeExited function to SC.State. During
SC.StatechartManager#gotoState, all states that will be exited will have
this function called. If any of them return NO, the state transition will
be canceled.