run more (simple) tests for (almost) all + improve partial updates test
(native) connection #columns #columns_internal expects string table_name
[db2] (finish up) XML column support
[mysql] version + support_"feature" (as Rails); align sql type mapping
groupd schema dump tests + generic schema dump tests (from Rails)
jdbc_connection unwrap parameter for unwrapping (pooled) connections
avoid unitialized instance var warning
some more schema_dump tests + standalone schema tests for postgres