Dropped "dark wake" support on OS X, which was preventing portables from going

Dropped "dark wake" support on OS X, which was preventing portables from going
to sleep when there was a stuck job. We now use a variation of the CUPS 1.4
sleep support to do a cleaner sleep (<rdar://problem/14323704>)

Aside from removing all of the power assertions, we now track a new
"cups-waiting-for-completed" state keyword that tells cupsd it can SIGKILL a
backend without side-effects - then if we are just waiting for the job to
complete we can go to sleep immediately.

git-svn-id: svn+ssh://src.apple.com/svn/cups/cups.org/trunk@11403 a1ca3aef-8c08-0410-bb20-df032aa958be