Generate mashals during build in libxfcegui4

[Nick Schermer]

Well I committed the fix, stuff shouldn't be there and it doesn't
break anything.

I think we should discuss libxfce4ui then. After the switch to wnck
there is too much deprecated code in gui4 and it's leaves its
footprint on most of the Xfce applications.

In fact, we could simply create a directory structure in svn, I
already have the basic code for libxfce4ui ready (without interfaces).
We can then, part by part, discuss that we're going to move over or
not.
Probably the best way to go since we had this discussion a number of times...

Nick