This adds a "Make Default" button in gnome-display-properties, which is used
to set up a systemwide default RANDR configuration. For users which don't have
a personal ~/.config/monitors.xml, then that systemwide configuration will
be used instead.
There is a PolicyKit helper program, gnome-display-properties-install-systemwide,
which is used to create the file
/etc/gnome-settings-daemon/xrandr/monitors.xml
in a secure fashion.
Otherwise we get:
/usr/bin/ld: gnome-mouse-properties.o: undefined reference to symbol 'floor@@GLIBC_2.0'
/usr/bin/ld: note: 'floor@@GLIBC_2.0' is defined in DSO /lib/libm.so.6 so try adding it to the linker command line
/lib/libm.so.6: could not read symbols: Invalid operation
https://bugzilla.gnome.org/show_bug.cgi?id=609570
