add paper_width, paper_height, and duplex parameters to ::begin.

add paper_width, paper_height, and duplex parameters to ::begin.

* backend/ev-ps-exporter.h: add paper_width, paper_height, and
duplex parameters to ::begin.

* tiff/tiff-document.c (tiff_document_ps_export_begin):
* shell/ev-print-job.c (idle_print_handler):
* ps/ps-document.c (ps_document_ps_export_begin):
* pdf/ev-poppler.cc (pdf_document_ps_exporter_begin):
* backend/ev-ps-exporter.c (ev_ps_exporter_begin): update
implementations. Poppler backend needs poppler cvs. Rest has
unchanged behavior.