[Tinyos Core WG] I-Frames on the CC2420

[Philip Levis]

I just checked in some changes that make I-Frames the default for the  
CC2420. To use T-Frames, you have to use the "tframe" make option.  
This means that code compiled for the CC2420 is not network-compatible  
with code before unless you use the tframe option. I also updated the  
15.4 base station app so you can select whether you want I-Frame  
support or not as a command-line parameter.

Phil