PR #1125 - more disturbing buried zombies

Pull request from entrez:  hero walking over a zombie's burial site
will only disturb it if meeting a minimum weight threshold.

Update several weight macros to be 'unsigned', matching mons[].cwt.
[I'm not sure about this one.  'unsigned short' promotes to 'signed
int' these days on most platforms.]

Closes #1125

include/permonst.h

@@ -30,9 +30,9 @@ struct attack {
 
 /*     Weight of human body, elf, dragon
  */
-#define WT_HUMAN 1450
-#define WT_ELF 800
-#define WT_DRAGON 4500
+#define WT_HUMAN 1450U
+#define WT_ELF 800U
+#define WT_DRAGON 4500U
 
 #ifndef ALIGN_H
 #include "align.h"

src/hack.c

@@ -2618,7 +2618,9 @@ domove_core(void)
                 nomul(0);
     }
 
-    if (!Levitation && !Flying && !Stealth)
+    /* your tread on the ground may disturb the slumber of nearby zombies */
+    if (!Levitation && !Flying && !Stealth
+        && gy.youmonst.data->cwt >= (WT_ELF / 2))
         disturb_buried_zombies(u.ux, u.uy);
 
     if (hides_under(gy.youmonst.data) || gy.youmonst.data->mlet == S_EEL