forward declarations for struct monst, struct obj

This should eliminate the 'onefile' complaint for objects.c without
breaking anything with any standard conforming compiler.  (Fingers
crossed.)

include/monst.h

@@ -6,6 +6,11 @@
 #ifndef MONST_H
 #define MONST_H
 
+/* start with incomplete types in case these aren't defined yet;
+   basic pointers to them don't need to know their details */
+struct monst;
+struct obj;
+
 #ifndef MEXTRA_H
 #include "mextra.h"
 #endif

include/obj.h

@@ -9,6 +9,11 @@
 /* #define obj obj_nh */ /* uncomment for SCO UNIX, which has a conflicting
                           * typedef for "obj" in <sys/types.h> */
 
+/* start with incomplete types in case these aren't defined yet;
+   basic pointers to them don't need to know their details */
+struct obj;
+struct monst;
+
 union vptrs {
     struct obj *v_nexthere;   /* floor location lists */
     struct obj *v_ocontainer; /* point back to container */

src/objects.c

@@ -2,8 +2,6 @@
 /* Copyright (c) Mike Threepoint, 1989.                           */
 /* NetHack may be freely redistributed.  See license for details. */
 
-struct monst { struct monst *dummy; };  /* lint: struct obj's union */
-
 #include "config.h"
 #include "obj.h"