Made SETI mode remove the continuum components. Because of the

Made SETI mode remove the continuum components.  Because of the
  continuous frequency-scanning, the continuum data will be invalid
  anyway, and of little use.

This saves a little bit of CPU, so I've been able to get a 25Khz
  FFT with a length of 32768 bins, for continued sub-1Hz resolution,
  but with a wider instantaneous bandwidth.  For some reason, though,
  there's a "knee" in the curve, and running at 50Khz sampling increases
  the CPU consumption by a much larger factor than you'd expect.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@3764 221aa14e-8319-0410-a670-987f0aec2ac5