[daip] selection

[Gustaaf Van Moorsel]

There seems to be a problem with how source selection interferes with
selection based on calcode, at least in the case of SPLIT.

1 - Using the - sign works: if one source name is preceded by a -
    none of the sources in the list are selected.

2 - Using the calcode works fine, too: is CALCODE='C', only sources
    with that calcode are selected.

3 - If one combines the two, and unselects only one source, it works:
    Only CALCODE 'C" sources are selected with the exception of the
    source specified with the minus sign.

4 - It seems to break down when more than one source is unselected:
    the source list is disregarded and all sources (with calcode 'C')
    are selected.

Gustaaf (in Dwingeloo, running 31DEC00 AIPS).