minetown guards outside the town proper

Pat forwarded a message from the newsgroup in March that the town guards
enforce rules even outside the town proper.  Fix: On room-based town levels,
check if the location is in a room containing subrooms (roomno will often
have a subroom id instead).  On the other levels (e.g. minetn-5), there are
no subrooms, so the whole level is fair game.  Currently, this is valid.
If fancier towns are added in the future, more flags or use of regions may
be required to tell where the town border actually is.  These checks are done
in a new in_town function.

include/extern.h

@@ -669,6 +669,7 @@ E void NDECL(domove);
 E void NDECL(invocation_message);
 E void FDECL(spoteffects, (BOOLEAN_P));
 E char *FDECL(in_rooms, (XCHAR_P,XCHAR_P,int));
+E boolean FDECL(in_town, (int,int));
 E void FDECL(check_special_room, (BOOLEAN_P));
 E int NDECL(dopickup);
 E void NDECL(lookaround);