Damage corpses by smashing them

Adds the ability to damage corpses by smashing them (implements #1322), and makes damaged corpses rez slower and less effectively.

The way I've currently set it up, your chance of successfully damaging a corpse is based on a combination of cutting damage and str+bash damage. The best pulping weapons have high cutting and bash damage, although cutting is a little more important than bashing. Axes, for instance, would be pretty good.

When you swing at corpses, it will target *all* corpses in the tile, although it may be sensible to apply some penalty to corpses other than the first.

Also has a bugfix for losing focus when your character isn't actually learning anything.