encoder: Fix int wrt protocol version

We can use BININT* opcodes only starting from protocol >= 1.
At protocol 0 we must use ASCII INT.

encode.go

@@ -263,6 +263,8 @@ func (e *Encoder) encodeFloat(f float64) error {
 func (e *Encoder) encodeInt(k reflect.Kind, i int64) error {
 	// FIXME: need support for 64-bit ints
 
+	// protocol >= 1: BININT*
+	if e.config.Protocol >= 1 {
 		switch {
 		case i > 0 && i < math.MaxUint8:
 			return e.emit(opBinint1, byte(i))
@@ -274,10 +276,11 @@ func (e *Encoder) encodeInt(k reflect.Kind, i int64) error {
 			var b = [1+4]byte{opBinint}
 			binary.LittleEndian.PutUint32(b[1:], uint32(i))
 			return e.emitb(b[:])
+		}
+	}
 
-	default: // int64, but as a string :/
+	// protocol 0: INT
 	return e.emitf("%c%d\n", opInt, i)
-	}
 }
 
 func (e *Encoder) encodeLong(b *big.Int) error {

ogorek_test.go

@@ -155,13 +155,16 @@ var tests = []TestEntry{
 		P2_("\x89.")), // NEWFALSE
 
 	X("int(5)", int64(5),
-		I("I5\n.")), // INT
+		P0("I5\n."),    // INT
+		P1_("K\x05.")), // BININT1
 
 	X("int(0x123)", int64(0x123),
-		I("I291\n.")), // INT
+		P0("I291\n."),      // INT
+		P1_("M\x23\x01.")), // BININT2
 
 	X("int(0x12345)", int64(0x12345),
-		I("I74565\n.")), // INT
+		P0("I74565\n."),            // INT
+		P1_("J\x45\x23\x01\x00.")), // BININT
 
 	X("float", float64(1.23),
 		I("F1.23\n.")), // FLOAT