Xfwm4 / compositor: gray background

[Olivier Fourdan]

Note that for a package (ie not a local build), it's probably easier
and safer to just create a simple patch to define MONITOR_ROOT_PIXMAP
in src/compositor.c, i.e something like:

#define MONITOR_ROOT_PIXMAP 1

in src/compositor.c along with the other defines, e.g. line 103:

http://git.xfce.org/xfce/xfwm4/tree/src/compositor.c?h=xfce-4.12#n103

Cheers,
Olivier