Fracking: Missed some setPatchColor -> patchChanged changes
Fracking,Water: Well patches retain their original type

This fixes some problems in the Water model where wells were being
treated as hard boundaries -- erasing layers didn't work as expected,
and water would not flow past a well pipe within the layers.
Fracking,Water: Better handling of well lookahead types
Wells: Remove redundant WELL_IMG definition
Fracking: Fix well drawing problem where well walls/interior aren't colored properly