Moving write errors out of return value into separate API methods.

write(), print(), println() now return size_t (and don't use negative values to signal errors).
Print adds writeError() for checking for write errors, clearWriteError() to reset the flag to false, and a protected setWriteError() for signalling errors.

http://code.google.com/p/arduino/issues/detail?id=598

libraries/LiquidCrystal/LiquidCrystal.h

@@ -79,7 +79,7 @@ public:
 
   void createChar(uint8_t, uint8_t[]);
   void setCursor(uint8_t, uint8_t); 
-  virtual ssize_t write(uint8_t);
+  virtual size_t write(uint8_t);
   void command(uint8_t);
 private:
   void send(uint8_t, uint8_t);