[daip] DTSUM and DiFX data

[Walter Brisken]

DiFX, the new software correlator that is to replace the VLBA correlator 
in the next few months, can produce data with integration times that are 
not restricted to be multiples of 131072 microseconds.

DTSUM seems to assume that it is an exact multiple of this:

Data integration time (cross-power) =  2.000000 =   15 * 0.131072 seconds
Data integration time (total-power) =  2.000000 =   15 * 0.131072 seconds

I'm not sure if displaying the "=   15 * 0.131072" is for information only 
or if internally it (or any other VLBI AIPS task) makes any assumption 
about the granularity of integration times in actual calculations.  I 
hope not!

-Walter