Convert in_storage() to a simple accessor (potentially XSifyable)
Move the infmap verification/exception way earlier

The thing deliberately is not a method on the source, because I am not
entirely sure where it belongs *YET*. Just knew it does not belong
in the (hopefully) extractable parser-gens.
Simplify collapse map contents, shuffle things around, rename most vars

There are almost no functional changes, just better organize what goes where
Yet another collapser oversight

One can't reuse collapsers across a left join
And another collapser issue

One can not infer definedness from the presence of a parent *unless* we have
a 'belongs_to'-like relationship to that parent
Optimization - order only on lazy prefetch

If the user wants all() without an order_by she doesn't care anyway
Reintroduce conditional null-branch pruning and add direct-to-HRI option

<massive commit message yet to come>