Fix basic debugging problems.

Fix basic debugging problems.

* Debugging
There are numerous problems, including no replies sent to messages and
incorrect replies.
- Added condition/report-string to the abort message.
- Added a DYNAMIC-WIND in the condition handler in the message handler
  for emacs-rex to ensure that the :abort message is always written,
  even when a restart is called.
- Added a global (fluid) binding *index* that is used to send the
  correct message index in the :debug message.

There are many problems remaining, to be tackled in a later commit.