[cups.general] Page accounting

[Matthias Clasen]

I tried to analyse why I don't see reasonable page accounting
information when I request "job-media-sheets" and
"job-media-sheets-completed" for my jobs. Here is what I found:

- Normally, pstops is responsible for emitting PAGE: m n messages,
  except if there is another filter specified in the ppd file, e.g.
  foomatic-rip
- In that case, foomatic-rip is reponsible for emitting PAGE: m n
  messages. To this end, it injects some PostScript code into the 
  job data which causes gs to emit PAGE: m n messages. 
- It then goes off to run the renderer using the cmdline specified
  in the ppd file. Unfortunately, the "renderer" is not gs, but cat
  if prefiltering is turned off for the queue...

Turning on prefiltering fixes this part, but then the ipp backend
emits a PAGE: total n line when it gets a "job-media-sheets-completed"
attribute back from the remote side.
Unfortunately, due to brokenness on the other side, the value is 0,
so the job-media-sheets-completed value gets set back to 0 by the
daemon. Shouldn't it maybe use MAX() there ?

I'm not quite sure which parts are just my misunderstanding how
page accounting is supposed to work, which parts are incompleteness
of the cups ipp implementation, and which are honest bugs...

Regards, Matthias