[daip] Request for FITLD modification for DiFX data

[Walter Brisken]

The software correlator produces output data that is nearly identical to 
that of the hardware correlator.  I have found one difference that 
requires a minor change to FITLD.

First, one can identify data produced by DIFX by looking at the FITS 
header.  There will be a line

CORR    = 'DIFX'

at the top.  Feel free to suggest alternatives to this if this is not 
appropriate.  I continue to set TELESCOP = VLBA and ORIGIN = VLBA 
Correlator.

The change requested for DiFX is as follows:  The digital saturation 
parameter, called SATUR in FITLD, should always be set to 1.0 for data 
from DiFX.  This parameter is very tersely described in vlba scientific 
memo 12.

As far as I can tell, all of the other corrections made for VLBA 
correlator data also apply to DiFX correlated data.

Thanks,

Walter