Use SDA and SCL constants, not hardcoded registers for TWI pullups.

http://code.google.com/p/arduino/issues/detail?id=601

Author: damellis

libraries/Wire/utility/twi.c

@@ -32,6 +32,7 @@
 #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
 #endif
 
+#include "pins_arduino.h"
 #include "twi.h"
 
 static volatile uint8_t twi_state;
@@ -63,18 +64,10 @@ void twi_init(void)
 {
   // initialize state
   twi_state = TWI_READY;
-
-  #if defined(__AVR_ATmega168__) || defined(__AVR_ATmega8__) || defined(__AVR_ATmega328P__)
-    // activate internal pull-ups for twi
-    // as per note from atmega8 manual pg167
-    sbi(PORTC, 4);
-    sbi(PORTC, 5);
-  #else
-    // activate internal pull-ups for twi
-    // as per note from atmega128 manual pg204
-    sbi(PORTD, 0);
-    sbi(PORTD, 1);
-  #endif
+  
+  // activate internal pullups for twi.
+  digitalWrite(SDA, 1);
+  digitalWrite(SCL, 1);
 
   // initialize twi prescaler and bit rate
   cbi(TWSR, TWPS0);