R1:3ce69b63067c

Allow Phabricator to write an access log using PhutilDeferredLog

Summary: Provide a configurable access log.

Test Plan:
Got a sensible-looking log including logged-in, logged-out, conduit, 404, etc:

[Mon, 23 Apr 2012 20:08:12 -0700] 32599 orbital - epriestley DifferentialCommentPreviewController - /differential/comment/preview/42/ http://local.aphront.com:8080/D42 200 65406
[Mon, 23 Apr 2012 20:08:12 -0700] 32881 orbital - epriestley DifferentialChangesetViewController …