Improve speed of [a v] lookups

[ncalexan]

Right now, <avs does a bunch of selects against all_datoms. It's super slow, since it's extremely inefficient to queryall_datoms for a textual match. This ticket tracks doing something less significant than #69 to speed this up. Namely:

• only query from all_datoms for fulltext attributes;
• consider using a temporary table and one big query rather than many small queries.

[rnewman]

@ncalexan is this still relevant with your rewrite?

[ncalexan]

No, this should be "efficient" if not "optimized".