Cleanup VirtualXact at end of Hot Standby

Resolves bug 7572 reported by Daniele Varrazzo

src/backend/storage/ipc/standby.c

@@ -103,6 +103,9 @@ ShutdownRecoveryTransactionEnvironment(void)
 
 	/* Release all locks the tracked transactions were holding */
 	StandbyReleaseAllLocks();
+
+	/* Cleanup our VirtualTransaction */
+	VirtualXactLockTableCleanup();
 }