[daip] DFTPL only averages IF 1

[Michael Rupen]

Dear DAIP,
  DFTPL seems to average only the first IF (for VLA data anyhow): at least
I got identical answers for DFTPL run on (1) a standard VLA continuum
data set with 2 IF pairs, and (2) the same data set, after UVCOPing just the 
1st IF.  DFTPL did give a different answer for the UVCOP of just the 2nd IF,
so there is a way around this, but it's kind of annoying.  So, suggestions
in order of ease & utility:

1- Fix the documentation to say PROMINENTLY that this task looks only at the
  first IF

2- Fix the task to average over all IFs by default

3- Add BIF/EIF to allow the user to select which IFs to average

The latter would be very useful; UVCOP is not a big deal, but it adds
another step which doesn't seem very necessary.

  Thanks,

         Michael