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/weapons.go

@@ -9,8 +9,8 @@ const noWeapon WeaponKind = -1
 // missile fires a missile in a given direction (weapons.c missile).
 func (g *RogueGame) missile(ydelta, xdelta int) {
 	// Get which thing we are hurling
-	obj := g.getItem("throw", KindWeapon)
-	if obj == nil {
+	obj, ok := g.promptPackItem("throw", KindWeapon)
+	if !ok {
 		return
 	}
 
@@ -113,8 +113,8 @@ func (g *RogueGame) wield() {
 
 	p.CurWeapon = oweapon
 
-	obj := g.getItem("wield", KindWeapon)
-	if obj == nil {
+	obj, ok := g.promptPackItem("wield", KindWeapon)
+	if !ok {
 		g.After = false
 
 		return
@@ -133,7 +133,7 @@ func (g *RogueGame) wield() {
 		return
 	}
 
-	sp := g.invName(obj, true)
+	sp := g.inventoryName(obj, true)
 	p.CurWeapon = obj
 
 	if !g.Options.Terse {