I can see use creating an nvl clone, but I don't see how to easily do
that to decode, since it can take an arbritary number of arguments.
We'd have to create a different decode function clone for each new
argument.
One thing that I want to ask is: are we going the easy, more
maintainable route of creating functions to mimick Oracle's (e.g. nvl)
or are we porting everything to PG's dialect? Supposedly the latter
would have better performance (?) but it'll be harder to synch with
aD's tree.
