Scope.runAsync should handle all the microtasks

[jbdeboer]

There is a bad interaction between NgZone and Scope, where if Scope.digest created a microtask, NgZone will run it and then force a brand-new Scope.digest run.

This causes too mach Scope.digests and can lead to infinite loops.

The best approach we have so far is to have Scope handle all the microtasks in its runAsync queue.

[mvuksano]

@jbdeboer Can you tell me if this is similar/same as #976 (mhevery@2675da0)? If it's not same, I have a feeling it might be very similar.

[jbdeboer]

It is; I have code for this issue, but haven't got around to writing the tests for Scope -- I suspect that the whole test suite should be refactored.