nerf potion alchemy (trunk only)

nerf potion alchemy (trunk only)

     Something I've had in mind for a long time:  make it harder to acquire
dozens of potions of full healing and thereby (8 * dozens) of extra hit
points.  When dipping a stack of more than 2 potions into another potion
other than water, first split the stack so that 2 to 9 potions are dipped
rather than all of them.  Alchemy still works but it will take more dips
(hence need more resources) to convert large amounts.  Dipping into water
isn't affected, nor is dipping non-potions.

     Also fix a bug where dipping a stack--now perhaps a subset stack after
splitting--which triggered an explosion was only using up one of the dipped
potions (plus the one being dipped into) instead of the whole stack.