canvap.py: added setViewerPreference stuff inspired by kevin@booksys.com
canvap.py: added setViewerPreference stuff inspired by kevin@booksys.com

makinacorpus/reportlab-ecomobile,makinacorpus/reportlab-ecomobile,makinacorpus/reportlab-ecomobile,makinacorpus/reportlab-ecomobile,makinacorpus/reportlab-ecomobile