Properly reset class variables in FITS-IDI filler (#1370)
In particular, clear the array name when processing the primary HDU.
This makes sure converting multiple FITS-IDI files from different
arrays will correctly identify the array and make the appropriate
digital corrections for the various array/correlator combinations.
Change the warning about conflicting observatory names to SEVERE
as this now only applies to conflicting names within a single
FITS-IDI file, which would be serious trouble as the wrong digital
corrections would probably be applied. This should not happen in
real life.
