Clean up lockmanager data structures some more, in preparation for planned

rewrite of deadlock checking.  Lock holder objects are now reachable from
the associated LOCK as well as from the owning PROC.  This makes it
practical to find all the processes holding a lock, as well as all those
waiting on the lock.  Also, clean up some of the grottier aspects of the
SHMQueue API, and cause the waitProcs list to be stored in the intuitive
direction instead of the nonintuitive one.  (Bet you didn't know that
the code followed the 'prev' link to get to the next waiting process,
instead of the 'next' link.  It doesn't do that anymore.)