avoid AS present? usage - :schema/:username set to empty is for the user to fix
+ also correctly detect programatic JNDI configuration (config[:data_source] set)
[db2] improve create_table on Z/OS (now supporting AR 4.x TableDefinition)

should fix #581
[postgres] rename the primary key index when renaming a table in pg

... from Rails: https://github.com/rails/rails/commit/1460470005f2d9