Generate mashals during build in libxfcegui4

[Nick Schermer]

Should, with the patch below, also the verinfo number be changed or
the package version raised? Although I guess nobody used the
netk-marshal functions, they are not public available anymore.

http://foo-projects.org/~nick/patches/xfcegui4-marshals.patch

Everything runs fine here, be I'm not entirely sure. So please sign-off ;-).

Cheers,
Nick