unicorn horn vs sustain ability (trunk only)

Forwarded from newsgroup by <Someone> in February, 2005:  non-cursed
unicorn horn fixes lost Str/Con/&c stats even when ring of sustain ability
is supposedly locking those at current value.  This makes unicorn horn
honor the Fixed_abil intrinsic.  The potion and spell of restore ability
still override that, so they now have potential for use even after player
has acquired a unihorn.  Prayer also continues to override Fixed_abil.
Major prayer result to heal crippled strength now attempts to uncurse a
ring of sustain ability (or gloves or weapon covering it up--similar
situation as with cursed levitation).  Minor prayer result to fix lost
stats resets those without attempting to do anything about Fixed_abil.

src/apply.c

@@ -1671,9 +1671,16 @@ struct obj *obj;
 
 	/* collect attribute troubles */
 	for (idx = 0; idx < A_MAX; idx++) {
+	    if (ABASE(idx) >= AMAX(idx)) continue;
 	    val_limit = AMAX(idx);
 	    /* don't recover strength lost from hunger */
 	    if (idx == A_STR && u.uhs >= WEAK) val_limit--;
+	    if (Fixed_abil) {
+		/* potion/spell of restore ability override sustain ability
+		   intrinsic but unicorn horn usage doesn't */
+		unfixable_trbl += val_limit - ABASE(idx);
+		continue;
+	    }
 	    /* don't recover more than 3 points worth of any attribute */
 	    if (val_limit > ABASE(idx) + 3) val_limit = ABASE(idx) + 3;