allows setting of fft size from command line when starting dspserver
default is 4096, if the option --fft is not invoked at startup.  If
used, the syntax is
--fft #### where #### can be any of 4096, 8192, 16384, 32768,
65536, 131072, or 262144.
As with the other options for dspserver, if one enters a nonsense option
such as --whatever, then a help message comes up that describes this and
the other options in detail.