Enabled serial console output during the install process.

Allows to monitor the install process through the serial port, in case the user has no display to connect the pi.

![screenshot - 30-05-2014 - 15 15 15](https://cloud.githubusercontent.com/assets/911097/3131477/e7bc55a2-e804-11e3-9a5f-293e589ff352.png)