Work on digital narrowband examples (and Issue 452)

I started trying to address issue 452 that would hopefully help with
some
of the problems people have with the digital narrowband examples when
the
transmitter and receiver’s frequencies are too far apart.

See my latest message for a potential resolution:
http://gnuradio.org/redmine/issues/452

In my tests, it works, but I’m looking for feedback on this proposed
solution.

Thanks,
Tom