[daip] imagr overwrites

[Lynn D. Matthews]

If I give imagr an output file name that already exists and set allokay=0,
I notice that the header of the re-imaged file will reflect changes in
various imagr parameters (e.g., beam size, number of iterations, or coord.
shifts). However, if the channel number changes, the frequency coordinate
and Alt ref. pixel both stay fixed to the values from the originally
imaged channel. Is there a reason why the frequency information does not
also update?