randr: set physical screen size to keep a constant 96 dpi
randr: set physical screen size to keep a constant 96 dpi

Some applications compute DPI based on physcial screen size.  Currently,
the width is reported to be 270mm, regardless of the resolution.  This
patch instead compute a physical screen size to have a constant DPI of
96. Of course, there are possible improvements to this approach (see
fixme), however, since that code is no longer executed with DRM driver,
I don't think we should invest more effort here (I guess DRM driver
relies on xrandr / gnome-settings-daemon to do the right thing, so
physical screen is updated)

https://bugzilla.redhat.com/show_bug.cgi?id=1066094

elmarco/vdagent-gtk,elmarco/vdagent-gtk,elmarco/vdagent-gtk