Summary: Ref T13395. Fixes a file-locking test and removes a logging test that's more trouble than it's worth.
Test Plan: Ran "arc unit --everything" locally, got a clean bill of health.
Maniphest Tasks: T13395
Differential Revision: https://secure.phabricator.com/D20984
Summary: Ref T13395. Moves all remaining code in "libphutil/" into "arcanist/".
Test Plan: Ran various arc workflows, although this probably has some remaining rough edges.
Maniphest Tasks: T13395
Differential Revision: https://secure.phabricator.com/D20980