cleanup handling of structure-template resource-list parsing.  It is
still very inefficient, and needs to be sorted out in short order, but
it should no longer be the main bottleneck at load time.  

slightly adjust how the 'water' validation type handles placement of air
blocks/water blocks as filler.  still need to come up with a good way to
tell the difference between 'air' and 'air but really water' fills in
the template (probably just break down and make people scan with the
water in them)