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.
Revert "Merge pull request #269 from mads379/parsetree-1001326"

The parse-tree changes have been merged in Scala [pull 1982](https://github.com/scala/scala/pull/1982),
so there is no need for it anymore. Moreover, the presentation compiler must *not* be interrupted
while parsing on a foreign thread, and that can't be ensured in this commit (but is correctly ensured
in the Scala changeset). Since this branch is used with 2.9.3, there is a potential for race conditions.

This reverts commit 712e6bf5eb983a18aac03294c0656519d53ac634, reversing
changes made to 4f7b391cf1a64c6d906263afc2ebd0928bf4cb4d.
(cherry picked from commit 209133c903f2b9edf1c84fea0060374e40ded9c8)
Merge pull request #327 from dragos/issue/debugger-shutting-down

More robust against VM exceptions.