Add parity and stop bit configuration for HardwareSerial on Arduino Due

[agdl]

From @cmaglie on April 2, 2013 22:38

This is currently not implemented:

Serial1.begin(9600, SERIAL_8N2);

relevant forum topic:
http://arduino.cc/forum/index.php/topic,156442.0.html

Copied from original issue: arduino/Arduino#1343