Push feed publishing deeper into the task queue

Summary:
Ref T2852. I want to model Asana integration as a response to feed events. Currently, we queue one feed event for each HTTP hook.

Instead, always queue one feed event and then have it queue any necessary followup events (now, http hooks; soon, asana).

Add a script to make it easy to reproducibly fire feed event publishing.

Test Plan:
Republished a feed event and verified it hit configured HTTP hooks correctly.

$ ./bin/feed republish 5765774156541908292 --trace
>>> [2] <connect> phabricator2_feed
<<< [2] <connect> 1,660 us
>>> [3] <query> SELECT story.* FROM `feed_storydata` story JOIN `feed_storyreference` ref ON ref.chronologicalKey = story.chronologicalKey WHERE (ref.chronologicalKey IN (5765774156541908292)) GROUP BY story.chronologicalKey ORDER BY story.chronologicalKey DESC
<<< [3] <query> 595 us
>>> [4] <connect> phabricator2_differential
<<< [4] <connect> 760 us
>>> [5] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [5] <query> 478 us
>>> [6] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [6] <query> 449 us
>>> [7] <connect> phabricator2_user
<<< [7] <connect> 1,062 us
>>> [8] <query> SELECT * FROM `user` WHERE phid in ('PHID-USER-lqiz3yd7wmk64ejugvov')
<<< [8] <query> 540 us
>>> [9] <connect> phabricator2_file
<<< [9] <connect> 951 us
>>> [10] <query> SELECT * FROM `file` WHERE phid IN ('PHID-FILE-gq6dlsysvxbn3dgwvky7')
<<< [10] <query> 498 us
>>> [11] <query> SELECT * FROM `user_status` WHERE userPHID IN ('PHID-USER-lqiz3yd7wmk64ejugvov') AND UNIX_TIMESTAMP() BETWEEN dateFrom AND dateTo
<<< [11] <query> 507 us
Republishing story...
>>> [12] <query> SELECT story.* FROM `feed_storydata` story JOIN `feed_storyreference` ref ON ref.chronologicalKey = story.chronologicalKey WHERE (ref.chronologicalKey IN (5765774156541908292)) GROUP BY story.chronologicalKey ORDER BY story.chronologicalKey DESC
<<< [12] <query> 685 us
>>> [13] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [13] <query> 489 us
>>> [14] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [14] <query> 512 us
>>> [15] <query> SELECT * FROM `user` WHERE phid in ('PHID-USER-lqiz3yd7wmk64ejugvov')
<<< [15] <query> 601 us
>>> [16] <query> SELECT * FROM `file` WHERE phid IN ('PHID-FILE-gq6dlsysvxbn3dgwvky7')
<<< [16] <query> 405 us
>>> [17] <query> SELECT * FROM `user_status` WHERE userPHID IN ('PHID-USER-lqiz3yd7wmk64ejugvov') AND UNIX_TIMESTAMP() BETWEEN dateFrom AND dateTo
<<< [17] <query> 551 us
>>> [18] <query> SELECT story.* FROM `feed_storydata` story JOIN `feed_storyreference` ref ON ref.chronologicalKey = story.chronologicalKey WHERE (ref.chronologicalKey IN (5765774156541908292)) GROUP BY story.chronologicalKey ORDER BY story.chronologicalKey DESC
<<< [18] <query> 507 us
>>> [19] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [19] <query> 428 us
>>> [20] <query> SELECT * FROM `differential_revision` WHERE phid IN ('PHID-DREV-ywqmrj5zgkdloqh5p3c5')
<<< [20] <query> 419 us
>>> [21] <query> SELECT * FROM `user` WHERE phid in ('PHID-USER-lqiz3yd7wmk64ejugvov')
<<< [21] <query> 591 us
>>> [22] <query> SELECT * FROM `file` WHERE phid IN ('PHID-FILE-gq6dlsysvxbn3dgwvky7')
<<< [22] <query> 406 us
>>> [23] <query> SELECT * FROM `user_status` WHERE userPHID IN ('PHID-USER-lqiz3yd7wmk64ejugvov') AND UNIX_TIMESTAMP() BETWEEN dateFrom AND dateTo
<<< [23] <query> 593 us
>>> [24] <http> http://127.0.0.1/derp/
<<< [24] <http> 746,157 us
[2013-06-24 20:23:26] EXCEPTION: (HTTPFutureResponseStatusHTTP) [HTTP/500] Internal Server Error

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2852

Differential Revision: https://secure.phabricator.com/D6291