changing available() to return an int (because the Ethernet Client class or another stream might need more than 255 bytes).

cores/arduino/HardwareSerial.cpp

@@ -173,7 +173,7 @@ void HardwareSerial::end()
   cbi(*_ucsrb, _rxcie);  
 }
 
-uint8_t HardwareSerial::available(void)
+int HardwareSerial::available(void)
 {
   return (RX_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail) % RX_BUFFER_SIZE;
 }

cores/arduino/HardwareSerial.h

@@ -48,7 +48,7 @@ class HardwareSerial : public Stream
       uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udre, uint8_t u2x);
     void begin(long);
     void end();
-    virtual uint8_t available(void);
+    virtual int available(void);
     virtual int peek(void);
     virtual int read(void);
     virtual void flush(void);

cores/arduino/Stream.h

@@ -26,7 +26,7 @@
 class Stream : public Print
 {
   public:
-    virtual uint8_t available() = 0;
+    virtual int available() = 0;
     virtual int peek() = 0;
     virtual int read() = 0;
     virtual void flush() = 0;