Clive Crous' Dark Room patch

This patch adds a new glyph that represents dark parts of room,
splitting the dual functionality of the "unexplored/dark area" glyph.

include/flag.h

@@ -23,6 +23,7 @@ struct flag {
 	boolean  biff;		/* enable checking for mail */
 	boolean  bones;		/* allow saving/loading bones */
 	boolean  confirm;	/* confirm before hitting tame monsters */
+	boolean  dark_room;	/* show shadows in lit rooms */
 	boolean  debug;		/* in debugging mode */
 #define wizard	 flags.debug
 	boolean  end_own;	/* list all own scores */