Make hostile monsters with launcher and ammo keep away

If a hostile monster is wielding a ranged weapon, and is carrying
appropriate ammo for it, make the monster try to stay away,
outside the melee range.

src/monmove.c

@@ -999,6 +999,12 @@ register int after;
                     > ((ygold = findgold(g.invent)) ? ygold->quan : 0L))))
             appr = -1;
 
+        /* hostile monsters with ranged thrown weapons try to stay away */
+        if (!mtmp->mpeaceful
+            && (dist2(mtmp->mx, mtmp->my, mtmp->mux, mtmp->muy) < 5*5)
+            && m_canseeu(mtmp) && m_has_launcher_and_ammo(mtmp))
+            appr = -1;
+
         if (!should_see && can_track(ptr)) {
             register coord *cp;