Simply because it's simpler.

Fixes the following that occurs with recent uhd changes.

UHDDevice.cpp:260: error: ‘struct uhd::gain_range_t’ has no member named ‘max’
UHDDevice.cpp:260: error: ‘struct uhd::gain_range_t’ has no member named ‘min’

This patch modifies the low level implementation to use uhd devices
instead of the usrp library from gnuadio. Also, edit the user
interface to reflect changes. Currently, only the USRP2 has been
tested.

http://thre.at/kalibrate/kal-v0.4.1.tar.bz2