fixed macro IS_PIN_INTERRUPT

Author: jnsbyr

Boards.h

@@ -678,7 +678,7 @@ writePort(port, value, bitmask):  Write an 8 bit port.
 #define IS_PIN_SERVO(p)         (IS_PIN_DIGITAL(p) && (p) < MAX_SERVOS)
 #define IS_PIN_I2C(p)           ((p) == SDA || (p) == SCL)
 #define IS_PIN_SPI(p)           ((p) == SS || (p) == MOSI || (p) == MISO || (p) == SCK)
-#define IS_PIN_INTERRUPT(p)     digitalPinToInterrupt(p)
+#define IS_PIN_INTERRUPT(p)     (digitalPinToInterrupt(p) > NOT_AN_INTERRUPT)
 #define IS_PIN_SERIAL(p)        ((p) == PIN_SERIAL_RX || (p) == PIN_SERIAL_TX)
 #define PIN_TO_DIGITAL(p)       (p)
 #define PIN_TO_ANALOG(p)        ((p) - A0)