merge this feature, and code cleanups for signal handlers,

from 2.1-dev:

      Add fatal exception hook for use by diagnostic modules.  The hook
      is only available if the --enable-exception-hook configure parm
      is used and the EnableExceptionHook directive has been set to
      "on".

Reviewed by:	stoddard, jerenkrantz, gregames


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@102786 13f79535-47bb-0310-9956-ffa450edef68