- added new method for compound-fields named "specs_unmodified"
- don't hard-code name "validator" in extend_slot
- rename former "extend_slot" to "extend_slot_default"  since its
  functionality is pretty specialized
- use new "extend_slot" from xotcl-core to allow
  update_attribute_from_slot for
   * title
   * description
   * text
   * publish_date
- bump version dependency to xotcl-core
- bump version number to 0.150