[daip] VBGLU and sort order etc

[Michael Bietenholz]

I just noticed that if you run VBGLU (31DEC09; yesterday) on two data
sets, both of which are in strict 'TB' order (not 'T?' labelled as
'TB'), then the VBGLU output is not necessarily in 'TB' order.

I think this happens when both data sets are missing some visibilities

Here's PRTUV output that shows what happens:

  Vis #     IAT      Ant  Su Fq U(klam) V(klam) W(klam)  etc

Part 1
   15292  0/16:19:27  2- 8  1  1   22127  -18513   26334
                     (2- 9 is missing from part 1 at this time-stamp)
   15293  0/16:19:27  2-10  1  1   28088    4454   15699

Part 2
   15165  0/16:19:27  2- 8  1  1   22252  -18618   26482
   15166  0/16:19:27  2- 9  1  1   24996  -15241   24813
   15167  0/16:19:27  2-10  1  1   28247    4479   15787

Both Part 1 and Part 2 are in TB order, but after VBGLU we have this

VBGLU:
   15292  0/16:19:27  2- 8  1  1   22127  -18513   26334
   15293  0/16:19:27  2-10  1  1   28088    4454   15699
...
   15330  0/16:19:27  2- 9  1  1   24855  -15156   24674
    with the last vis. being now out of TB order.

So probably VBGLU matches up PT1 vis with their corresponding PT2
bits, writes them out, and then processes any missed bits in PT2.

This isn't really a problem, only the sort order on output is wrongly
set to 'TB'.  So it might be good if VBGLU set the sort-order on
output to 'T' (or, more elaborately, checked for this condition,
and set sort-order to 'T' only if order has got changed).

Also, perhaps VBGLU should write its AIPS version into the history?

          cheers, michael