Address github issue #983 - getpos valid locations

Issue reported by entrez:  when getpos() is being used to have the
player pick a map location, if player types '$' (for some operations
like jumping or applying a polearm) then valid spots are highlighted
but the highlighting obscures what was shown on the map.  I'm not
sure whether this 'fixes' the issue but it's probably good enough.
Allow typing another '$' to toggle the highlighting back off,
redisplaying the map in the process, without needing to move the
cursor or type ^R to accomplish that.  Toggling seems more intuitive.

This is a lot more complicated than it needs to be because I assumed
that the background aspect of highlighting stayed visible when the
glyphs were reverted.  It doesn't work that way but I haven't thrown
out the effort to make toggling the highlights work sanely.  Prior
to this, typing '$' again just redrew the highlighting again, with
no visible effect.

Closes #983

doc/fixes3-7-0.txt

@@ -1489,6 +1489,9 @@ hallucination of objects incorrectly included generic objects as candidates
 	for what objects looked like; if an object had its dknown flag set,
 	formatting a generic object in its place was unreliable (Null pointer
 	deference prior to static analyzer fix, odd fake name "generic" after)
+some actions that ask the user to pick a location allow typing '$' to show
+	valid spots, accept typing a second '$' prior to moving the cursor to
+	toggle the highlights off; ^R already did that; moving the cursor too
 
 curses: 'msg_window' option wasn't functional for curses unless the binary
 	also included tty support