[net2-wg] CC1000 white bit

[Philip Levis]

I've added an initial implementation of the CC1000 white bit (as well  
as the CC2420 white bit) to the main tree. The CC2420 white bit is  
the value we've used in our experiments (105), while the CC1000  
threshold is a value I came up with after looking at some data  
sheets. The CC1000 one definitely needs sanity checking by someone  
who has a bunch of mica2s, which I don't (Kyle?).

Phil