More robust against VM exceptions.

* clearly report an actor shutting down because of an uncaught exception
  using the Eclipse Error log
* gracefully handle the common VM exceptions.

This is not exhaustive (a handful of FIXME notes are still in the codebase),
but it is a step in the right direction and fixes a number of issues I've
been seeing lately.

Fixed #1001328, Refs #1001487.
Merge pull request #327 from dragos/issue/debugger-shutting-down

More robust against VM exceptions.