Improvements

1. Support for setting Oracle session attributes and similar.
2. Transaction isolation parameter will now default to a globally configured value allowing the administrator to set a site wide default. Macro parameters can still override the default value. The global default is the same (READ_COMMITTED) as the former macro default, so it is upward compatible with existing usage. Administrators should be careful changing the default as it will apply to all existing macros that have not specifically overridden the existing default. For instance, macros that still need READ_COMMITTED after the global default is changed to something else, will need to be changed to select the specific READ_COMMITTED value.