Validate all components of $PATH configuration

Summary: Fixes T3400. Users are crafty. Attempt to outwit them.

Test Plan: Added all kinds of nonsense to my PATH to hit all the errors. Verified sensible-looking error messages which I couldn't figure out any way to misread or outwit.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T3400

Differential Revision: https://secure.phabricator.com/D6318
Allow filtering maniphest tasks authored by agents

Summary:
Addes a button group to filter tasks by agents, non-agents or all.

Fixes T3394

Test Plan: View task list, filter by agents, filter by non agents. Make sure the correct tasks display.

Reviewers: epriestley, dctrwatson

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3394

Differential Revision: https://secure.phabricator.com/D6328
Construct diffs with attached changesets, even if empty

Summary: See discussion in IRC. Not 100% sure what's going on here because of email ghost theives, but conceivably a commit with no changes will end up with `null` changesets instead of `array()` changesets, which throws. Such diffs are certianly possible (`git commit --allow-empty`) even if they aren't the issue in this specific case. See T3416. Initialize changesets to `array()` to avoid throwing.

Test Plan:
Viewed some commits?

iiam

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6339