Cleaned up the job processing code (now use a shared process management

Cleaned up the job processing code (now use a shared process management
function).

The client code didn't zero the request file descriptor, which caused
problems with job processing.

The SIGCLD handler didn't reset the signal handler so some signals were
getting lost.

Implemented StopPrinter().

UpdateJobs() and sigcld_handler() now stop the printer or cancel the job
as needed when an error occurs.

git-svn-id: svn+ssh://src.apple.com/svn/cups/cups.org/trunk@218 7a7537e8-13f0-0310-91df-b6672ffda945