final(?) touchstone

final(?) touchstone
     Put back the "better gold handling" that was inadvertently
dropped from the previous rewrite.  Prevent gems rubbed on cursed
gray stones other than touchstones from being shattered.  Fix
several pluralization buglets, including allowing the player to
rub a stone against itself if the quantity is more than one (just
like potion dipping is handled).  Overall, streamline the rather
convoluted logic, eliminating the `goto's.