Add support for MySQL notifications (fixes #3818) (#3907)

As a new configuration parameter is added, configuration version is
bumped up from 14 to 15.

The MySQL target's behaviour is identical to the PostgreSQL: rows are
deleted from the MySQL table on delete-object events, and are
created/updated on create/over-write events.

vendor/vendor.json

@@ -80,6 +80,12 @@
 			"revision": "0d253a66e6e1349f4581d6d2b300ee434ee2da9f",
 			"revisionTime": "2017-02-16T21:49:44Z"
 		},
+		{
+			"checksumSHA1": "QD6LqgLz2JMxXqns8TaxtK9AuHs=",
+			"path": "github.com/go-sql-driver/mysql",
+			"revision": "2e00b5cd70399450106cec6431c2e2ce3cae5034",
+			"revisionTime": "2016-12-24T12:10:19Z"
+		},
 		{
 			"checksumSHA1": "3yco0089CSJ4qbyUccpbDC2+dPg=",
 			"path": "github.com/gogo/protobuf/gogoproto",