howmonseen - monster visibility (trunk only)

Pull some code out of lookat() so that it can be used elsewhere.
howmonseen(mon) returns a bitmask of the ways that hero can see mon.

include/extern.h

@@ -2402,6 +2402,7 @@ E void FDECL(unblock_point, (int,int));
 E boolean FDECL(clear_path, (int,int,int,int));
 E void FDECL(do_clear_area, (int,int,int,
 			     void (*)(int,int,genericptr_t),genericptr_t));
+E unsigned FDECL(howmonseen, (struct monst *));
 
 #ifdef VMS
 

include/vision.h

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)vision.h	3.5	1995/01/26	*/
+/*	SCCS Id: @(#)vision.h	3.5	2007/05/11	*/
 /* Copyright (c) Dean Luick, with acknowledgements to Dave Cohrs, 1990. */
 /* NetHack may be freely redistributed.  See license for details.	*/
 
@@ -55,4 +55,13 @@ extern char *viz_rmax;			/* max could see indices */
 /* Use this macro to get a list of distances of the edges (see vision.c). */
 #define circle_ptr(z) (&circle_data[(int)circle_start[z]])
 
+/* howmonseen() bitmask values */
+#define MONSEEN_NORMAL		0x0001	/* normal vision */
+#define MONSEEN_SEEINVIS	0x0002	/* seeing invisible */
+#define MONSEEN_INFRAVIS	0x0004	/* via infravision */
+#define MONSEEN_TELEPAT		0x0008	/* via telepathy */
+#define MONSEEN_XRAYVIS		0x0010	/* via Xray vision */
+#define MONSEEN_DETECT		0x0020	/* via extended monster detection */
+#define MONSEEN_WARNMON		0x0040	/* via type-specific warning */
+
 #endif /* VISION_H */