smartcontract: always use int64 for integers

It is good when internal representation is unique.

pkg/smartcontract/param_type.go

@@ -181,7 +181,7 @@ func adjustValToType(typ ParamType, val string) (interface{}, error) {
 			return nil, errors.New("invalid boolean value")
 		}
 	case IntegerType:
-		return strconv.Atoi(val)
+		return strconv.ParseInt(val, 10, 64)
 	case Hash160Type:
 		u, err := address.StringToUint160(val)
 		if err == nil {

pkg/smartcontract/param_type_test.go

@@ -185,15 +185,15 @@ func TestAdjustValToType(t *testing.T) {
 	}, {
 		typ: IntegerType,
 		val: "0",
-		out: 0,
+		out: int64(0),
 	}, {
 		typ: IntegerType,
 		val: "42",
-		out: 42,
+		out: int64(42),
 	}, {
 		typ: IntegerType,
 		val: "-42",
-		out: -42,
+		out: int64(-42),
 	}, {
 		typ: IntegerType,
 		val: "q",

pkg/smartcontract/parameter_test.go

@@ -384,13 +384,13 @@ func TestNewParameterFromString(t *testing.T) {
 		out: Parameter{StringType, "qwerty"},
 	}, {
 		in:  "42",
-		out: Parameter{IntegerType, 42},
+		out: Parameter{IntegerType, int64(42)},
 	}, {
 		in:  "Hello, 世界",
 		out: Parameter{StringType, "Hello, 世界"},
 	}, {
 		in:  `\4\2`,
-		out: Parameter{IntegerType, 42},
+		out: Parameter{IntegerType, int64(42)},
 	}, {
 		in:  `\\4\2`,
 		out: Parameter{StringType, `\42`},
@@ -399,7 +399,7 @@ func TestNewParameterFromString(t *testing.T) {
 		out: Parameter{StringType, `\42`},
 	}, {
 		in:  "int:42",
-		out: Parameter{IntegerType, 42},
+		out: Parameter{IntegerType, int64(42)},
 	}, {
 		in:  "true",
 		out: Parameter{BoolType, true},