xrandr: Don't check for hi-dpi on monitors with broken EDID

If the monitor reports a width/height that looks suspiciously like an
aspect ratio (16/9 or 16/10) don't check for hi-dpi. We can assume that
makers of devices that do support hi-dpi aren't so careless.

See http://cgit.freedesktop.org/~daniels/xserver/commit/?h=lodpi

https://bugzilla.gnome.org/show_bug.cgi?id=738748