ppdFilterPSToPS(): Fixed reverse output order

With PPD files for PostScript printers or for (proprietary) driver
filters requiring PostScript input (for example Brother) and where the
printer which stacks the printed paper face-up and therefpre needs
reverse output order for correct stacking ("*DefaultOutputOrder:
Reverse" in PPD) there was no output at all. ppdFilterPSToPS() turned
the PostScript input file into empty, zero-bytes output.

The empty output is due to a wrong function being used for the
output. This was most probably introduced with the conversion of the
pstops CUPS filter to the ppdFilterPSToPS() filter function. At too
many places the regular puts()/printf() got replaced by
doc_puts()/doc_printf() where actually just a fputs()/fprintf() to
outputfd had been needed.

This is corrected now and we get correct output for these PPD files
again.

Fixes #20: #20