chain summoning

This adds a further throttle to chain summoning.  Monsters can only summon
spellcasting nasties if the nasties are lower level than the summoner, which
makes infinite chains impossible (as long as the player figures out which
monster to kill first).

doc/fixes34.1

@@ -54,7 +54,7 @@ avoid dmonsfree impossible message due to migrating a dead monster via
 avoid temporary disappearing Burdened message due to updating status line
 	midway thru in_container
 don't credit player's wisdom when makelevel creates random Elbereth engravings
-reduce insect/monster creation from monster spells
+reduce insect/monster creation from monster spells and limit chain summons
 avoid "couldn't place lregion type 5" warning when arriving at Plane of Fire
 avoid crash due to delayed poly or were change no longer being valid
 ensure that Priest's ability to recognize B/U/C is considered in B/U/C menus

src/wizard.c

@@ -10,6 +10,8 @@
 #include "hack.h"
 #include "qtext.h"
 
+extern const int monstr[];
+
 #ifdef OVLB
 
 STATIC_DCL short FDECL(which_arti, (int));
@@ -435,10 +437,19 @@ nasty(mcast)
 	bypos.y = u.uy;
 	for(i = rnd(tmp); i > 0; --i)
 	    for(j=0; j<20; j++) {
+		int makeindex;
+
 		if (mcast &&
 			!enexto(&bypos, mcast->mux, mcast->muy, mcast->data))
 		    continue;
-		if ((mtmp = makemon(&mons[pick_nasty()],
+		/* Don't create more spellcasters of the monsters' level or
+		 * higher--avoids chain summoners filling up the level.
+		 */
+		do {
+		    makeindex = pick_nasty();
+		} while(mcast && attacktype(&mons[makeindex], AT_MAGC) &&
+			monstr[makeindex] >= monstr[mcast->mnum]);
+		if ((mtmp = makemon(&mons[makeindex],
 				    bypos.x, bypos.y, NO_MM_FLAGS)) != 0) {
 		    mtmp->msleeping = mtmp->mpeaceful = mtmp->mtame = 0;
 		    set_malign(mtmp);