#13 bw-raspidefs_2.1.5 Raspberry Pi control lines for DDL

[Bernd Wagner]

Raspberry Pi has only UART interface(s), but no support for some RS232 control lines like DTR or RI.
This patch allows to use Raspberry's GPIOs as RS232 control lines for DDL, if the booster needs so.
see README.raspberrypi for more explanation.