Rejigger anti-magic traps

My changes were too drastic, so reduce the drain and damage so it
matches all the other traps. Now the anti-magic trap will always
ding your max energy a bit, in addition to the physical damage done
if wearing magic resistance.

doc/fixes3-7-0.txt

@@ -533,8 +533,7 @@ dying from being level-drained below level 1 killed hero without saying so
 	and jumped straight to "do you want your possessions identified?"
 conflict will now consider your charisma and requires line of sight
 boost hit points of some golems
-make anti-magic fields drain more energy and prevent them from showing up
+make anti-magic fields always drain max energy
-	too early in the dungeon
 eating magical monsters such as wizards or shamans may give a mild buzz
 make exploding spheres create an actual explosion
 pets are more careful about attacking monsters at low health

src/mklev.c

@@ -1435,7 +1435,6 @@ mktrap(
                 if (lvl < 5)
                     kind = NO_TRAP;
                 break;
-            case ANTI_MAGIC:
             case LANDMINE:
                 if (lvl < 6)
                     kind = NO_TRAP;

src/trap.c

@@ -2037,17 +2037,13 @@ trapeffect_anti_magic(
     unsigned int trflags UNUSED)
 {
     if (mtmp == &g.youmonst) {
-        int drain = (u.uen > 1) ? (rnd(u.uen / 2) + 2) : 4;
+        int drain = d(2, 6);
+        int halfd = rnd(((drain + 1) / 2));
 
         seetrap(trap);
-        /* hero without magic resistance loses spell energy,
+        if (Antimagic) {
-           hero with magic resistance takes damage instead;
-           possibly non-intuitive but useful for play balance */
-        if (!Antimagic) {
-            drain_en(drain);
-        } else {
             struct obj *otmp;
-            int dmgval2 = rnd(drain), hp = Upolyd ? u.mh : u.uhp;
+            int dmgval2 = rnd(4), hp = Upolyd ? u.mh : u.uhp;
 
             /* Half_XXX_damage has opposite its usual effect (approx)
                but isn't cumulative if hero has more than one */
@@ -2074,6 +2070,11 @@ trapeffect_anti_magic(
             /* opposite of magical explosion */
             losehp(dmgval2, "anti-magic implosion", KILLED_BY_AN);
         }
+        if (u.uenmax > halfd) {
+            u.uenmax -= halfd;
+            drain -= halfd;
+        }
+        drain_en(drain);
     } else {
         boolean trapkilled = FALSE;
         boolean in_sight = canseemon(mtmp) || (mtmp == u.usteed);
@@ -2084,7 +2085,7 @@ trapeffect_anti_magic(
         if (!resists_magm(mtmp)) { /* lose spell energy */
             if (!mtmp->mcan && (attacktype(mptr, AT_MAGC)
                                 || attacktype(mptr, AT_BREA))) {
-                mtmp->mspec_used += d(2, 2);
+                mtmp->mspec_used += d(2, 6);
                 if (in_sight) {
                     seetrap(trap);
                     pline("%s seems lethargic.", Monnam(mtmp));