Provide a script to completely destroy revisions

Summary:
Someone may or may not have accidentally uploaded secrets to Differential. Provide an administrative mechanism to permanently destroy a revision.

Also fix some of the transaction handling code.

Test Plan:
  $ ./scripts/differential/destroy_revision.php --trace D1
  >>> [0] <connect>
  <<< [0] <connect> 1,060 us
  >>> [1] <query> SELECT * FROM `differential_revision` WHERE `id` = 1
  <<< [1] <query> 473 us

      Really destroy 'D1: asdbas' forever? [y/N] y

  >>> [2] <connect>
  <<< [2] <connect> 628 us
  >>> [3] <query> START TRANSACTION
  <<< [3] <query> 190 us
  >>> [4] <query> SELECT * FROM `differential_diff` WHERE revisionID = 1
  <<< [4] <query> 510 us
  >>> [5] <query> SAVEPOINT Aphront_Savepoint_1
  <<< [5] <query> 122 us
  >>> [6] <query> SELECT * FROM `differential_changeset` WHERE diffID = 1
  <<< [6] <query> 307 us
  >>> [7] <query> SAVEPOINT Aphront_Savepoint_2
  <<< [7] <query> 241 us
  >>> [8] <query> SELECT * FROM `differential_hunk` WHERE changesetID = 1
  <<< [8] <query> 212 us
  >>> [9] <query> DELETE FROM `differential_hunk` WHERE `id` = 1
  <<< [9] <query> 216 us
  >>> [10] <query> DELETE FROM `differential_changeset` WHERE `id` = 1
  <<< [10] <query> 154 us
  >>> [11] <query> SAVEPOINT Aphront_Savepoint_2
  <<< [11] <query> 118 us
  >>> [12] <query> SELECT * FROM `differential_hunk` WHERE changesetID = 2
  <<< [12] <query> 194 us
  >>> [13] <query> DELETE FROM `differential_hunk` WHERE `id` = 2
  <<< [13] <query> 179 us
  >>> [14] <query> DELETE FROM `differential_changeset` WHERE `id` = 2
  <<< [14] <query> 163 us
  >>> [15] <query> SAVEPOINT Aphront_Savepoint_2
  <<< [15] <query> 105 us
  >>> [16] <query> SELECT * FROM `differential_hunk` WHERE changesetID = 3
  <<< [16] <query> 211 us
  >>> [17] <query> DELETE FROM `differential_hunk` WHERE `id` = 3
  <<< [17] <query> 159 us
  >>> [18] <query> DELETE FROM `differential_changeset` WHERE `id` = 3
  <<< [18] <query> 152 us
  >>> [19] <query> SAVEPOINT Aphront_Savepoint_2
  <<< [19] <query> 124 us
  >>> [20] <query> SELECT * FROM `differential_hunk` WHERE changesetID = 4
  <<< [20] <query> 191 us
  >>> [21] <query> DELETE FROM `differential_hunk` WHERE `id` = 4
  <<< [21] <query> 155 us
  >>> [22] <query> DELETE FROM `differential_changeset` WHERE `id` = 4
  <<< [22] <query> 149 us
  >>> [23] <query> SELECT * FROM `differential_diffproperty` WHERE diffID = 1
  <<< [23] <query> 242 us
  >>> [24] <query> DELETE FROM `differential_diffproperty` WHERE `id` = 1
  <<< [24] <query> 196 us
  >>> [25] <query> DELETE FROM `differential_diff` WHERE `id` = 1
  <<< [25] <query> 169 us
  >>> [26] <query> DELETE FROM `differential_relationship` WHERE revisionID = 1
  <<< [26] <query> 178 us
  >>> [27] <query> DELETE FROM `differential_commit` WHERE revisionID = 1
  <<< [27] <query> 164 us
  >>> [28] <query> SELECT * FROM `differential_comment` WHERE revisionID = 1
  <<< [28] <query> 221 us
  >>> [29] <query> DELETE FROM `differential_comment` WHERE `id` = 1
  <<< [29] <query> 172 us
  >>> [30] <query> SELECT * FROM `differential_inlinecomment` WHERE revisionID = 1
  <<< [30] <query> 296 us
  >>> [31] <query> SELECT * FROM `differential_auxiliaryfield` WHERE revisionPHID = 'PHID-DREV-ooky7ozqukpmwget32oc'
  <<< [31] <query> 308 us
  >>> [32] <query> SELECT * FROM `differential_affectedpath` WHERE revisionID = 1
  <<< [32] <query> 4,173 us
  >>> [33] <query> DELETE FROM `differential_revision` WHERE `id` = 1
  <<< [33] <query> 231 us
  >>> [34] <query> COMMIT
  <<< [34] <query> 686 us
  OK, destroyed revision.

Reviewers: csilvers, vrana, jungejason

Reviewed By: csilvers

CC: aran

Differential Revision: https://secure.phabricator.com/D2796