Make XAssetService a de-duplicating asset service.

This is an extremely crude implemenation which almost works by accident.  Nevertheless it does work.
It can be tested with the instructions at http://opensimulator.org/wiki/Feature_Proposals/Deduplicating_Asset_Service#Testing
It does not interact at all with the existing asset service or any data stored there.
This code is subject to change without notice and should not be used for anything other than gawking.

OpenSim/Data/MySQL/Resources/XAssetStore.migrations

@@ -0,0 +1,27 @@
+# -----------------
+:VERSION 1
+
+BEGIN;
+
+CREATE TABLE `xassetsmeta` (
+  `id` char(36) NOT NULL,
+  `hash` char(64) NOT NULL,
+  `name` varchar(64) NOT NULL,
+  `description` varchar(64) NOT NULL,
+  `asset_type` tinyint(4) NOT NULL,
+  `local` tinyint(1) NOT NULL,
+  `temporary` tinyint(1) NOT NULL,
+  `create_time` int(11) NOT NULL,
+  `access_time` int(11) NOT NULL,
+  `asset_flags` int(11) NOT NULL,
+  `creator_id` varchar(128) NOT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='Version 1';
+
+CREATE TABLE `xassetsdata` (
+  `hash` char(64) NOT NULL,
+  `data` longblob NOT NULL,
+  PRIMARY KEY (`hash`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='Version 1';
+
+COMMIT;