[Libvir] bug in the virSetErrorFunc() function

[Philippe Berthault]

I've written a program based on libvirt (release 0.1.0) in which I uses the
virSetErrorFunc() function to avoid messages on the screen but one message
is always displayed (on stderr) and isn't trapped by the 
virSetErrorFunc() function.

This message is "Unimplemented block at xs_internal.c:255"

Thanks,