Completed support of retina displays for Fl_Paged_Device::print_window_part().
Case with high resolution parent window and low resolution GL window is now directly processed.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10485 ea41ed52-d2ee-0310-a9c1-e6b18d33e121