Rename item-subsystem methods (refactor step 5, items)

getItem→promptPackItem now returns (obj, ok) instead of a nil-signaling
pointer; invName→inventoryName; doPot→applyPotionFuse. C breadcrumbs
kept. Behavior unchanged; suite green.

game/rings.go

@@ -7,9 +7,9 @@ import "fmt"
 // ringOn puts a ring on a hand (rings.c ring_on).
 func (g *RogueGame) ringOn() {
 	p := &g.Player
-	obj := g.getItem("put on", KindRing)
+	obj, ok := g.promptPackItem("put on", KindRing)
 	// Make certain that it is something that we want to wear
-	if obj == nil {
+	if !ok {
 		return
 	}
 
@@ -65,7 +65,7 @@ func (g *RogueGame) ringOn() {
 		g.addmsgf("you are now wearing ")
 	}
 
-	g.msg("%s (%c)", g.invName(obj, true), obj.PackCh)
+	g.msg("%s (%c)", g.inventoryName(obj, true), obj.PackCh)
 }
 
 // ringOff takes off a ring (rings.c ring_off).
@@ -103,7 +103,7 @@ func (g *RogueGame) ringOff() {
 	}
 
 	if g.dropCheck(obj) {
-		g.msg("was wearing %s(%c)", g.invName(obj, true), obj.PackCh)
+		g.msg("was wearing %s(%c)", g.inventoryName(obj, true), obj.PackCh)
 	}
 }