Need to specify what happens in out of memory and stack situations

[gbracha]

The spec is currently silent on what happens if an isolate runs out of heap or stack space.

Possibilities include:

1. Throwing an exception (which could be caught by the Dart program). Experience from other languages indicates this is probably undesirable.
2. Terminate the isolate.
3. Suspend the isolate, and notify its spawner. This would likely be accomplished via an isolate lifecycle API that that reported on isolate death or near-death. We need such an API in any case.

TBD.

[gbracha]

How to report isolate death is still undecided. For the time being, the spec has been modified to state that an isolate that runs out of heap or stack causes an error that may not be caught, which in turn causes suspension of the isolate.

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Added Done label.