Add Throw and ReThrow nodes. Rethrow not yet tested (bailout with untested), since it needs the try…

Add Throw and ReThrow nodes. Rethrow not yet tested (bailout with untested), since it needs the try/catch implementation. Discuss if Throw/ReThrow shoudl be computations or instructions. We have one case in parser where throw is added into the expression tree.

I suggest introducing an EndInstr that has no successor and use it for throw and return. (TODO: Discuss and chnage if necessary). Currently we generate code even after the throw.
Committed: https://code.google.com/p/dart/source/detail?r=5490

[regis, 2012-03-14 21:24:01]

LGTM