Fixes to FilePrinter for Qt 4.4:

1) detectCupsService() finally works because QTCPSocket finally works. Assumes Cups is on localhost:631 which is a compromise as Qt won't even tell us if it is using Cups, let alone where Cups is.

2) Duplex printing obeys user selected option from dialog rather than just guessing.

3) If custom page margins set then respect these