SCUBA2: append suffix if called from PICARD
SCUBA2: restore original order to processing steps

In my last change I forgot a couple of things: 1) that the output
suffix was now unique and so wouldn't cause confusion, and 2) that the
whitening step must take place on the signal coadd first because the
size of the whitening region (used when whitening the psf and the
jack-knife map) must be determined from this image.
SCUBA2: retrieve the jack-knife map before proceeding

To ensure that the file naming convention is correct (in PICARD
anyway), the jack-knife map should be retrieved before whitening it
and calculating its noise properties.
SCUBA2: trap bad status from sc2filtermap

sc2filtermap can fail on maps that have been filtered too heavily (and
thus there is insufficient 1/f component to fit). Trap that status and
issue an error message. The recipe should proceed as normal hereafter,
but of course the output products will not be whitened.