libcupsfilters: Add input-page-ranges attribute to pdftopdf()

libcupsfilters: Add input-page-ranges attribute to pdftopdf()

Pull request #444

The page-ranges option/attribute applies to the putput page stream going to the printer. If an 8-page input document is printed with number-up=2 one gets 4 sheets, with input pages 1+2, 3+4, 5+6, and 7+8, applying page-ranges=1,4 in addition will give a sheet with input pages 1+2 and 7+8. This way you can easily repeat sheets if they failed to print correctly on the first attempt to print the job.

There was no way to select for example page 1-3 and page 6 from the input and arrange it on 2 sheets with 1+2 and 3+6, for example if only these pages contain exercises which you have to solve. or content relevant for your exam. This is now solved by adding the new input-page-ranges attribute. If you now print with "input-page-ranges=1-3,6 number-up=2" you get exactly what you want (Issue #365).