- added Imager's memory debugging code in an attempt to find the

 - added Imager's memory debugging code in an attempt to find the
   crash problem on Win32.  This seems to have eliminated the crash
   even when it's disabled (and just calls malloc/free/realloc)
   https://rt.cpan.org/Ticket/Display.html?id=18543
 - found the memory leak - we were creating an SV for the id to
   priority hash and nothing was releasing it
   https://rt.cpan.org/Ticket/Display.html?id=20018
 - the memory leak fix has become obsolete, we now avoid creating the
   SV at all by using the id in memory as a key to the hash.
 - added a verify method during debugging, it's not necessary anymore
   but someone else fiddling with the code might find it useful
 - pq_find_item() and pq_insertion_point() now use a binary search for
   larger queues.  These were the hotspots going by sprof profiling.