The JdbcCache.derivative_image_table configuration key has been renamed
to JDBCCache.variant_image_table.
Add and implement the jdbcsource_last_modified() method from the sample
delegate script.
If you are using a Java delegate, you must implement the new invoke()
method in such a way that it can invoke any of the four delegate methods
(including the new jdbcsource_last_modified()).
If you are using JDBCCache, change the DATETIME-type columns to
TIMESTAMP.
If you are using JDBCCache, add a TIMESTAMP-type last_modified column
to the image and info tables.