Adodb 5.20.x upgrade missing support for table alter in xmlschema.

We have alter table definitions in DatabaseSchema.xml

<table name="vtiger_blocks" alter="true">
		<constraint>ADD CONSTRAINT fk_1_vtiger_blocks FOREIGN KEY (tabid) REFERENCES vtiger_tab(tabid) ON DELETE CASCADE</constraint>
		<opt>Engine=InnoDB</opt>
		<data>
		</data>
	</table>

Adodb 5.20.x ends up building CREATE TABLE ... instead of ALTER TABLE ...