Provide a new "hint" table for weird commits (rewritten, unreadable)

Summary:
Ref T11522. This provides storage for tracking rewritten commits (new feature) and unreadable commits (existing feature, but really hacky).

This doesn't do anything yet, just adds a table and a CLI tool for updating it. I'll document the tool once it works. You just pipe in some JSON, but I need to document the format.

Test Plan:
  - Piped JSON for "none", "rewritten" and "unreadable" hints into `bin/repository hint`.
  - Examined the database to see that the table was written properly.
  - Tried to pipe bad JSON in, invalid hint types, etc. Got reasonable human-readable error messages.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11522

Differential Revision: https://secure.phabricator.com/D16434

resources/sql/autopatches/20160824.repohint.01.hint.sql

@@ -0,0 +1,8 @@
+CREATE TABLE {$NAMESPACE}_repository.repository_commithint (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  repositoryPHID VARBINARY(64) NOT NULL,
+  oldCommitIdentifier VARCHAR(40) NOT NULL COLLATE {$COLLATE_TEXT},
+  newCommitIdentifier VARCHAR(40) COLLATE {$COLLATE_TEXT},
+  hintType VARCHAR(32) NOT NULL COLLATE {$COLLATE_TEXT},
+  UNIQUE KEY `key_old` (repositoryPHID, oldCommitIdentifier)
+) ENGINE=InnoDB, COLLATE {$COLLATE_TEXT};