Bug fixes:
----------

- Revamp signals so that signals-to-threads more closely mimic linux
  operation.
  First step of fix for: http://cygwin.com/ml/cygwin/2012-05/msg00186.html

- Revert to only creating a new session leader when we know that a
  console process is started in the background.
  Should fix: http://cygwin.com/ml/cygwin/2012-08/threads.html#00062

- Fix mysterious crashes when accessing /etc.
  Fixes: http://cygwin.com/ml/cygwin/2012-07/threads.html#00613 and others.