more wizard mode wishing for terrain

more wizard mode wishing for terrain

Try a lot harder to keep terrain/level flags in a sane state.  They're
overloaded so it's not simple.

Creating a fountain or sink incremented the corresponding counter (for
controlling ambient sounds) but removing one by wishing for something
else in its place didn't decrement.

Allow wish for "disturbed grave" to create a grave with the 'disturbed'
flag set, similar to existing "magic fountain" and 'blessedftn' flag.
(I didn't add "looted throne", "looted tree", and several other things
that use the 'looted' overload of 'rm.flags'.)

Automate block_point (tree, cloud, secret corridor, or secret door in
open doorway) and add unblock_point (use Pass_wall to move into wall
or tree or stone, or just walk onto a cloud, then make iron bars or
almost any other wishable terrain to replace the blocking feature).