Remove "fault" module.

Remove "fault" module.

This module, which catches segmentation faults and prints a backtrace
before exiting, was useful for a while, but I believe that it has now
outlived its purpose.  It is altogether better to have a core dump from
which one can extract much more information than a usually-poor backtrace,
and core dumps are much better integrated into a typical Unix system.
In addition, the "fault" module was of course not all that portable.