r5691: wrapping the pause/resume/purge printer commands in

r5691: wrapping the pause/resume/purge printer commands in
{become,unbecome}_root() blocks.  We've already done
a print_access_check() to ensure the user is admin.
The means that non-root users can pause and manage printers.
I really don't see how this worked before without setuid
binaries on the server.

Also update print_queue_update() interface to allow an smbd
to update the print queue cache locally rather than going through
the bg lpq daemon.  This is needed for things like pjob_delete()
to ensure the cache is current for the specific client.
(This used to be commit f75369ec865f4ba1ae8201ae750c0f45158ed536)