Make closing attacks create gaps

Use up monster turns when they launch closing attacks. Basically ends
up similar to old random energy, but with less waiting (on average)
and slightly clearer/more explicit effects.

Author: PleasingFungus

crawl-ref/source/mon-act.cc

@@ -3129,20 +3129,20 @@ static bool _monster_swaps_places(monster* mon, const coord_def& delta)
     return false;
 }
 
-static bool _mons_closing_attack(monster& mons, coord_def delta)
+static void _mons_closing_attack(monster& mons, coord_def delta)
 {
     // XXX: should check reach instead of a fixed distance 1?
     if (mons.confused() || mons_is_batty(mons) || mons.foe_distance() > 1)
-        return false;
+        return;
     if (!one_chance_in(6))
-        return false;
+        return;
     actor* foe = mons.get_foe();
     ASSERT(foe); // else, how is foe distance <= 0?
     if (!mons.can_see(*foe))
-        return false;
+        return;
     coord_def old_pos = mons.pos() - delta;
     if (adjacent(old_pos, foe->pos()))
-        return false;
+        return;
 
 
     const string name = foe->name(DESC_THE);
@@ -3152,26 +3152,14 @@ static bool _mons_closing_attack(monster& mons, coord_def delta)
                                     mons.pronoun_plurality() ? "" : "s");
     simple_monster_message(mons, msg.c_str());
 
-    const energy_use_type move_type = _get_swim_or_move(mons);
-    const int move_cost = mons.energy_cost(move_type);
-
-    const int old_speed = mons.speed_increment;
     if (foe->is_player())
     {
         monster *ru_target = nullptr;
         if (_handle_ru_melee_redirection(mons, &ru_target))
-        {
-            mons.speed_increment -= move_cost; // XXX: should be non_move_energy
-            return true;
-        }
-
+            return;
         _melee_attack_player(mons, ru_target);
     } else
         fight_melee(&mons, foe);
-
-    const int speed_after_moving = old_speed - move_cost;
-    mons.speed_increment = min(mons.speed_increment, speed_after_moving);
-    return true;
 }
 
 static bool _do_move_monster(monster& mons, const coord_def& delta)
@@ -3299,8 +3287,8 @@ static bool _do_move_monster(monster& mons, const coord_def& delta)
 
     _handle_manticore_barbs(mons);
 
-    if (!_mons_closing_attack(mons, delta))
-        _swim_or_move_energy(mons);
+    _swim_or_move_energy(mons);
+    _mons_closing_attack(mons, delta);
 
     return true;
 }