Porting the NETWM classes to xcb

[Fredrik Höglund]

I have pushed an update to this branch that moves the xcb includes to
the .cpp file as suggested by Christoph.  I also fixed some 64 vs 32 bit
issues discovered by Philipp Knechtges while testing.

It's apparently also an issue that some Linux distributions are shipping
old versions of xcb that are missing some of the libraries the cmake
test checks for.  Right now the only library kdelibs is using is the core
xcb library.  This will change over time though, so I'm not sure what the
best way is to deal with this.

Is anyone else planning on testing and/or reviewing these patches?

Fredrik