Pixel "perSpool" option

[tresf]

Currently raw printing allows a "perSpool" option to split large batches into smaller, more reasonably sized batches.

Certain Pixel jobs may benefit from this option as well. For example, a client is printing > 1,000 pages, but they must wait for the entire job to spool before printing starts.

The proposal is to spool documents in smaller batches (e.g. 10, 100, 500) so that the spooler can begin printing while the next jobs begins the spooling process.

[tresf]

Testing #728, I'm able to observe spooling occurring at 30-seconds into the print, versus about 5 minutes.

Testing was done on a Windows 7 x86_64 machine with 4GB of RAM.

Some changes have been requested on the PR prior to merge.