Make some improvements to Cronscript.pm.

Make some improvements to Cronscript.pm.

Allow the session method to function when called more than once with
different service names.

Add some useful new methods:

logout: Calls open-ils.auth.session.delete if we're logged in.

die_event: Causes a script to croak if the object passed in is an event,
or optionally a certain named event.

warn_event: Causes a script to output an error message if the object passed
in is an event, or optionally a certain named event.

Use OpenILS::Application::AppUtils.

Default to staff login in Cronscript->authenticate method.

Improve the Croncript.pm.in POD to include a better synopsis of its features.

Clean up some other sections of the POD, remove the TODO section, and add
some SEE ALSO entries.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>