Order by core libs first in search results

[Thimoteus]

Mentioned here it'd be nice if names from core libs were displayed at the top, for example searching for apply, the definition of <*> isn't shown until the fourth listing.

[hdgarrood]

Perhaps it would be better to use number of reverse dependencies, i.e. a search result gets a small boost if it appears in a package which has more reverse dependencies (see also #292); that should achieve what's wanted here but also be useful for results outside of the core libraries.