Log Message:
Update to 5.23.  Changes:
* Fixed a bug in speed tests which would cause the grep implementation to
  fail.
* Fixed incorrect output for emails without message bodies.
* Fixed filename output for -n, -m and other situations when input comes
  from standard input.
* Added -w flag to match word boundaries.
* A warning is now issued and caching is disabled if -C is not specified
  and $HOME is not set (as might be the case when running grepmail in a
  cron job).