[daip] bug

[Chris Flatters]

> I've notice in uvcop - if you ask to copy a freqid that is not
> int hte data, it seems to take ages to come back and tell you
> it's not there, i.e. is it reading the whole dataset, not using the
> index table or something? (I'm assuming index tables carry freqid info).

UVCOP uses frequency ID information from the index table, if present, to
guess the size of the output file but doesn't make any other use of this
information. I think it is feasible to make UVCOP quit if it calculates
the number of output visibilities as zero and I will put this on my to-do
list.

	Chris