Since X440 is special in terms of operation in different Nyquist zones
users may stumble upon unexpected RF performance compared to other
devices if frequencies are chosen close to a Nyquist boundary. The
guided mode provides more information about the Nyquist zone in which
the chosen frequency is located in the info log. For disabling the
guided mode, `guided_mode=false` can be added to the UHD config file
in the "Global" section.
This adds a specialization to `uhd::cast::from_str()` to handle `bool`
as a target type and interpret strings like 'y', 'Y', 'n', 'No', 'True',
'False', etc. as Boolean values, as well as the traditional '0' and '1'
(which also work).
