Sanguino compile patch

@daapp : Sanguino compile serial USART path. Thanks!

serial.c

@@ -91,7 +91,11 @@ void serial_write(uint8_t data) {
 }
 
 // Data Register Empty Interrupt handler
+#ifdef __AVR_ATmega644P__
+ISR(USART0_UDRE_vect)
+#else
 ISR(USART_UDRE_vect)
+#endif
 {
   // Temporary tx_buffer_tail (to optimize for volatile)
   uint8_t tail = tx_buffer_tail;
@@ -140,7 +144,11 @@ uint8_t serial_read()
   }
 }
 
+#ifdef __AVR_ATmega644P__
+ISR(USART0_RX_vect)
+#else
 ISR(USART_RX_vect)
+#endif
 {
   uint8_t data = UDR0;
   uint8_t next_head;