Jump to PHP docs from symbol search more often

Summary:
It's kind of nice to type s explode in jump nav and have it
just work. This involves weakening a bunch of the request parameter
checks, but the only real extra assumption is that language defaults to
PHP... which is not that big of a stretch, and it's not like we know
about any other languages' documentation.

It'd be better to have builtins be more first-class and less awkward
hack, but that seems hard.

Test Plan: Search for symbols.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3302