Filename conventions for pipeline:

Want to achieve something like: expId.state.classId.ext

where expId is the unique exposure identifier;
      state is the state of processing for that file;
      classId is the class identifier, specifying a particular component of the exposure; and
      ext is an extension indicating the type of file (e.g., fits).

Constraint: classId cannot split components known only by the caller
(pmFPAfile groups all of these into the {OUTPUT} variable).

This constraint does not hinder us, since having the classId as the
last element before the extension makes it simple to get all
components of an exposure at a particular processing state.

Some realisations:

Input is typically:	expId.classId.fits

Detrend processed:	expId.detproc.detID.classId.fits
Detrend stats:		expId.detproc.detID.classId.stats
Stacked detrend:	camera.detType.detId.iter.classId.fits
Stacked stats:		camera.detType.detId.iter.classId.fits
Normalised stack:	camera.detType.norm.detId.iter.classId.fits
Detrend residual:	expId.detresid.detId.iter.classId.fits
Residual stats:		expId.detresid.detId.iter.classId.stats
Residual, bin 1:	expId.detresid.detId.iter.classId.b1.fits
Residual, bin 2:	expId.detresid.detId.iter.classId.b2.fits
Residual list, bin 1:	expId.detresid.detId.iter.b1.list
Residual list, bin 2:	expId.detresid.detId.iter.b2.list
JPEG, bin 1:		expId.detresid.detId.iter.b1.jpg
JPEG, bin 1:		expId.detresid.detId.iter.b2.jpg

Phase 2 processed:	expId.p2.classId.fits




Requirements:

Explain PPIMAGE.OUTPUT, PPIMAGE.BIN1, PPIMAGE.BIN2, etc.
