introduce support for coloring the frame behind a map location

Also includes support by paxed for polearm targeting using the
frame color.

Also renames USE_TILES to TILES_IN_GLYPHMAP which is a more
accurate description.

Not all window interfaces have full support for the color framing
of the background square yet.

MS-DOS needs further work (to bring it to both VESA and VGA, with
and without tiles.

Windows GUI is missing support.

X11 and Qt have been started, but may require further refinement.

dat/opthelp

@@ -106,7 +106,7 @@ altmeta        For unix and VMS, treat two character sequence
                "ESC c" as M-c (Meta+c, 8th bit set) when nethack  [False]
                obtains a command from player's keyboard.
 
-Boolean option if USE_TILES was set at compile time (MSDOS protected mode):
+Boolean option if TILES_IN_GLYPHMAP set at compile time (MSDOS):
 preload_tiles  control whether tiles get pre-loaded into RAM at    [True]
                the start of the game.  Doing so enhances performance
                of the tile graphics, but uses more memory.