Autobk with clamps runs in about ~60 milliseconds on
   Rabbit (Quad Xeon E5440, 2.8GHz, 4Gb RAM, 32-bit Windows 7)
   Macbook Probit (2.66GHz Intel Core 2 Duo, 4 Gb RAM, Mac OS 10.6.8)

That is, 100 runs of test_autobk (read datafile, autobk, fft, filter) takes
around 6 seconds.  Each run goes roughly as:

  ~10 msec to read file
  ~50 msec for autobk
   ~3 msec for 2 FFTs (forward and back transform)

For reference, Ifeffit takes about 100 milliseconds for the same operations.

Larch (pure Python) is ~2x faster than Ifeffit (pure Fortran).

Tests do not include graphics (100 ms or so)