Redundant comms

Here's my pull request for the redundant communication system as described here: http://paparazzi.enac.fr/wiki/Redundant_Communication

This currently provides redundancy for plane to ground communication only (not ground to plane). 

Since my last e-mail, I've added support for multiple aircraft sharing a link as well as displaying link status information during a replay.

- Cameron Lee (cam.w.lee@gmail.com)

![Screenshot from 2013-04-15 22:59:01](https://f.cloud.github.com/assets/2513285/433967/f1127c30-af07-11e2-8911-59fe72cf785c.png)