Improve Correlated Query Implementation

[psbrandt]

Right now our correlated query implementation is pretty limited. We only support a single relationship, and we match on specific resource/attribute pairs.

I think the more correct way to do this is to push aliases onto a stack in the context, and then process the where clause as a normal expression. This would eliminate the need for special resource/attribute pair matching and would re-use all the code we already have for expression translation.

When processing the where expression, when we encounter an alias reference, we would able to resolve this by peeking into the stack in the context. Basically, aliases are noted and resolved like any other reference.