WFS 2.0 cascaded stored query

Support for cascaded stored query backed layers from wfs-ng datastores.
Ah, I didn't know of that. I actually did override the "+" operator (only in this context!) so that it can concatenate strings (and combinations of strings and numbers) as well. It makes for much nicer expressions in this context, but might be in vain if there is a multi parameter concatenation function. Should I remove the overridden operator?