go/zodb: Fix Persistent.badf

Due to forgotten ... it was not passing prepared argv as argv to
fmt.Errorf, but as a single slice argument. The result was messy, for
example

    persistent_test.go:176: deactivate refcnt < 0: panic error unexpected:
        have: "[t.zodb.MyObject 000000000000000c](%!s(MISSING)): deactivate: refcnt < 0"
        want: "t.zodb.MyObject(000000000000000c): deactivate: refcnt < 0"

Using the occasion add details to deactivate refcnt panic, which
made me to discover this bug.

go/zodb/persistent.go

@@ -246,7 +246,7 @@ func (obj *Persistent) PDeactivate() {
 
 	obj.refcnt--
 	if obj.refcnt < 0 {
-		panic(obj.badf("deactivate: refcnt < 0"))
+		panic(obj.badf("deactivate: refcnt < 0  (= %d)", obj.refcnt))
 	}
 	if obj.refcnt > 0 {
 		return // users still left
@@ -310,7 +310,7 @@ func (obj *Persistent) istate() Ghostable {
 // badf returns formatted error prefixed with obj's class and oid.
 func (obj *Persistent) badf(format string, argv ...interface{}) error {
 	return fmt.Errorf("%s(%s): "+format,
-		append([]interface{}{obj.zclass.class, obj.oid}, argv...))
+		append([]interface{}{obj.zclass.class, obj.oid}, argv...)...)
 }
 
 

go/zodb/persistent_test.go

@@ -163,6 +163,22 @@ func TestPersistent(t *testing.T) {
 	obj2 := &Unregistered{}
 	assert.Equal(ClassOf(obj2), `ZODB.Go("lab.nexedi.com/kirr/neo/go/zodb.Unregistered")`)
 
+	// deactivate refcnt < 0  -> panic
+	func() {
+		defer func() {
+			r := recover()
+			if r == nil {
+				t.Fatal("deactivate refcnt < 0: not panicked")
+			}
+			ehave := fmt.Sprintf("%s", r)
+			ewant := fmt.Sprintf("t.zodb.MyObject(%s): deactivate: refcnt < 0  (= -1)", Oid(12))
+			if ehave != ewant {
+				t.Fatalf("deactivate refcnt < 0: panic error unexpected:\nhave: %q\nwant: %q", ehave, ewant)
+			}
+		}()
+
+		obj.PDeactivate()
+	}()
 
 	// TODO activate	- jar has to load, state changes
 	// TODO activate again	- refcnt++