[Tweener] try...catch-es

[Makc]

catching errors in onupdate/oncomplete makes it difficult to debug
those handlers, since debugger does not stop there and continues code
execution. it _may_ be good idea in release swf (though the idea of
code throwing errors does not sound good in 1st place, plus error
catching is extremely slow), but could you give us some sort of
"pleaseThrowMyErrors" switch so we wouldn't have to go there and
comment it out manually?