MR: !53

This is because to_tsquery doesn't work with multiple words not
separated by AND or OR.

This reverts commit 29ee1972.

It introduces a bug, it should not be merged.

However, the code doesn't work currently.

This has couple of drawbacks:
- we use postgres-simple and a raw sql query, opaleye would be better
I guess
- there is a hack for empty query, this should be replaced by
removing the WHERE clause in this case

Limit, offset, search string, order by.

This turned out to be quite heavy because of module import cycles.