[winswitch] Improvements to the xpra_Xdummy script for Arch Linux

[Antony Lee]

I can't seem to register on Trac so I'll post this here:

On Arch Linux, Xorg is a wrapper script

basedir=/usr/lib/xorg-server
if [ -x "$basedir"/Xorg.wrap ]; then
        exec "$basedir"/Xorg.wrap "$@"
else
        exec "$basedir"/Xorg "$@"
fi

neither /usr/lib/xorg-server/Xorg{,.wrap} are currently taken into account
by the xpra_Xdummy script; I'd suggest adding a few lines similar to the
special-casing done for Fedora.

Also, in my case I find that I need to append -configdir /some/dummy/path
to the invocation of xpra_Xdummy (in the xvfb line of xpra.conf) to get rid
of the following fatal error at startup:
(EE) xf86OpenConsole: Cannot open /dev/tty0 (No such file or directory)

Best,
Antony