encoder: Fix list wrt protocol version

- we can use EMPTY_LIST only if protocol >= 1

Also: since we are now using EMPTY_LIST only optionally, it is logical
to switch to

	MARK + ... + LIST

instead of

	EMPTY_LIST (or MARK + LIST @proto=0) + MARK + ... + APPENDS

which is at least 1 byte longer.

For the reference - APPENDS is also from protocol 1, while LIST is from
protocol 0.

encode.go

@@ -213,7 +213,14 @@ func (e *Encoder) encodeArray(arr reflect.Value) error {
 
 	l := arr.Len()
 
-	err := e.emit(opEmptyList, opMark)
+	// protocol >= 1: ø list -> EMPTY_LIST
+	if e.config.Protocol >= 1 && l == 0 {
+		return e.emit(opEmptyList)
+	}
+
+	// MARK + ... + LIST
+	// TODO detect cycles and double references to the same object
+	err := e.emit(opMark)
 	if err != nil {
 		return err
 	}
@@ -226,7 +233,7 @@ func (e *Encoder) encodeArray(arr reflect.Value) error {
 		}
 	}
 
-	return e.emit(opAppends)
+	return e.emit(opList)
 }
 
 func (e *Encoder) encodeBool(b bool) error {

ogorek_test.go

@@ -204,9 +204,14 @@ var tests = []TestEntry{
 		I("((I1\nI2\ntp0\n(I3\nI4\ntp1\ntp2\n.")),
 
 	X("list([])", []interface{}{},
+		P0("(l."), // MARK + LIST
+		P1_("]."), // EMPTY_LIST
 		I("(lp0\n.")),
 
 	X("list([1,2,3,True])", []interface{}{int64(1), int64(2), int64(3), true},
+		P0("(I1\nI2\nI3\nI01\nl."),    // MARK + INT + INT(True) + LIST
+		P1("(K\x01K\x02K\x03I01\nl."), // MARK + BININT1 + INT(True) + LIST
+		P2_("(K\x01K\x02K\x03\x88l."), // MARK + BININT1 + NEW_TRUE + LIST
 		I("(lp0\nI1\naI2\naI3\naI01\na.")),
 
 	X("str('abc')", "abc",