Pass down to lpr the printer margins

This makes automagically work the printing on printers with
hard-margins since the QPrinter dialog margins are initialized to the printer
hard-margins. If you still want the old and mostly unuseful
behaviour of not having any margin (and thus your printer not printing things on the borders) you
can always set the margins to 0 in the dialog

BUGS: 319476
FIXED-IN: 4.12.0