Decompose remaining effects-file hot spots (refactor step 7)

drain gains drainReaches; zapSpeed gains hasteTarget/slowTarget;
readHoldMonster gains holdMonstersNear; readCreateMonster gains
createMonsterSpot; revealSpot splits into revealChar/revealWall/
revealSolid/revealFloor; turnSee gains showSensed. potions.go,
scrolls.go, and sticks.go are complexity-clean. Behavior and RNG call
order unchanged.

game/potions.go

@@ -298,22 +298,8 @@ func (g *RogueGame) turnSee(turnOff bool) bool {
 			if !canSee {
 				g.addch(mp.OldCh)
 			}
-		} else {
-			if !canSee {
-				g.standout()
-			}
-
-			if !g.Player.On(Hallucinating) {
-				g.addch(mp.Type)
-			} else {
-				g.addch(g.randomMonsterLetter())
-			}
-
-			if !canSee {
-				g.standend()
-
-				addNew = true
-			}
+		} else if g.showSensed(mp, canSee) {
+			addNew = true
 		}
 	}
 
@@ -326,6 +312,29 @@ func (g *RogueGame) turnSee(turnOff bool) bool {
 	return addNew
 }
 
+// showSensed draws one monster for monster sense, standout when it is
+// otherwise invisible; it reports whether the monster was newly revealed
+// (the turn-on arm of the C turn_see loop).
+func (g *RogueGame) showSensed(mp *Monster, canSee bool) bool {
+	if !canSee {
+		g.standout()
+	}
+
+	if !g.Player.On(Hallucinating) {
+		g.addch(mp.Type)
+	} else {
+		g.addch(g.randomMonsterLetter())
+	}
+
+	if !canSee {
+		g.standend()
+
+		return true
+	}
+
+	return false
+}
+
 // seenStairs reports whether the player has seen the stairs (potions.c
 // seen_stairs).
 func (g *RogueGame) seenStairs() bool {