Timeout handling and recovery in loop() function now operative.
Start-up check for I2C signals short to ground added.
Initial I2C device probe speed up.
Possible infinite loops in I2C AVR native driver during fault conditions removed.
Reduce the time spent with interrupts disabled in I2CManager response code by enabling interrupts after the state machine has finished.
Also, some comment changes.
* Re-enable native I2C driver.
* Minor non-functional changes to native I2C Manager.
* Minor changes to make variable types explicit in comparisons.
* Fix IODevice::loop() to avoid null pointer dereference.
Strange problems with LCD driver tracked down to being caused by a call to p->_loop() when p is NULL.
* Correct sense of comparison in LCN support function Turnout::setClosedStateOnly()
* Remove code (now unused) from LCD driver.
* Add I2C textual error messages.
* Add I2C textual error messages.
* Fix compile error in 4809 I2C driver.
* Remove init function call from SSD1306 driver.
loop() contains startTransaction which is called after handleInterrupt(). However, startTransaction is called within handleInterrupt so remove the extra call. This appears to solve strange problems encountered with the LCD display.
