slamdata/slamengine — pull request #462 by sellout (2014-11-21 22:36:39+00:00)
Title: Add a default “is true” selector.

Fixes #320.

This causes us to prefer `$project; $match` over a `$where` selector,
preventing us from falling into a map/reduce (as long as the condition
can be represented as a Mongo `$project` expression).

Also lets us filter on a constant … which is _maybe_ useful somehow?