Merge branch 'master' into ide-1.5.x

Conflicts:
	hardware/arduino/cores/arduino/HardwareSerial.cpp
	hardware/arduino/cores/robot/Arduino.h

cores/arduino/HardwareSerial.cpp

@@ -152,7 +152,7 @@ void HardwareSerial::end()
 
 int HardwareSerial::available(void)
 {
-  return (int)(SERIAL_RX_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail) % SERIAL_RX_BUFFER_SIZE;
+  return ((unsigned int)(SERIAL_RX_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail)) % SERIAL_RX_BUFFER_SIZE;
 }
 
 int HardwareSerial::peek(void)

cores/arduino/HardwareSerial.h

@@ -32,6 +32,8 @@
 // using a ring buffer (I think), in which head is the index of the location
 // to which to write the next incoming character and tail is the index of the
 // location from which to read.
+// NOTE: a "power of 2" buffer size is reccomended to dramatically
+//       optimize all the modulo operations for ring buffers.
 #if !(defined(SERIAL_TX_BUFFER_SIZE) && defined(SERIAL_RX_BUFFER_SIZE))
 #if (RAMEND < 1000)
 #define SERIAL_TX_BUFFER_SIZE 16