Summary: Fixes T3857. Earlier work made this trivial and just left product questions, which I've answered by requiring the daemons to run on reasonable installs.
Test Plan: Ran `bin/search index` and `bin/search index --background`. Observed indexes write in the former case and tasks queue in the latter case. Commented with a unique string on a revision and searched for it a moment later, got exactly one result (that revision), verifying that reindexing works correctly.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T3857
Differential Revision: https://secure.phabricator.com/D7966
