Fix bug [2874791], Merfolk stat change issues

Fix some conditions causing permanent stat loss or gain for Mf with stat modifying boots.

Unmerge boots when the player starts levitating or flying on a water square.

Use move_player_to_grid in blink, semi-controlled blink, and teleportation.

Also fix a bug where Mf could random teleport into solid walls.

Created by  Charles Otto  on October 16, 2009
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