B14014: soft hats and piercers

Soft "helmets" don't protect against falling rocks, but did protect against
piercers.  Update the checks so only hard (metallic) helmets provide this
protection.  The same report quibbled about using the word "helmet" for
soft head coverings.  This patch does not address that quibble.

doc/fixes34.1

@@ -311,6 +311,7 @@ use get_adjacent_loc() rather than getdir() directly for some things where
 minor experience calculation tweaks
 level telporting out of the dungeon while carrying unpaid shop goods would
 	trigger "not on any bill" warnings during final inventory disclosure
+only hard helmets protect against falling piercers
 
 
 Platform- and/or Interface-Specific Fixes

src/hack.c

@@ -1493,7 +1493,7 @@ stillinwater:;
 			      Amonnam(mtmp), ceiling(u.ux,u.uy));
 			if(mtmp->mtame) /* jumps to greet you, not attack */
 			    ;
-			else if(uarmh)
+			else if(uarmh && is_metallic(uarmh))
 			    pline("Its blow glances off your helmet.");
 			else if (u.uac + 3 <= rnd(20))
 			    You("are almost hit by %s!",

src/mhitu.c

@@ -356,6 +356,7 @@ mattacku(mtmp)
 		u.uundetected = 0;
 		if (is_hider(youmonst.data)) {
 		    coord cc; /* maybe we need a unexto() function? */
+		    struct obj *obj;
 
 		    You("fall from the %s!", ceiling(u.ux,u.uy));
 		    if (enexto(&cc, u.ux, u.uy, youmonst.data)) {
@@ -377,7 +378,8 @@ mattacku(mtmp)
 		    if (youmonst.data->mlet != S_PIERCER)
 			return(0);	/* trappers don't attack */
 
-		    if (which_armor(mtmp, WORN_HELMET)) {
+		    obj = which_armor(mtmp, WORN_HELMET);
+		    if (obj && is_metallic(obj)) {
 			Your("blow glances off %s helmet.",
 			               s_suffix(mon_nam(mtmp)));
 		    } else {