Add syncmail support to pass through -p
--show-c-function options to the "cvs diff" command.
Changes in more detail:
* trivially add -p / --show-c-function parameters to
* pass through the parameter to the "cvs diff" command
* document changes in syncmail __doc__ and
* recompiled doc/syncmail.sgml to doc/syncmail.1
This does not look very complicated, so I rate the
probability this introduces bugs as low. A first test
at libexif CVS indicates it works as intended.