- Fixed a variety of synonym()-related regressions

  - Fixed a variety of synonym()-related regressions
    from 0.6:
        - making a synonym against a synonym now works.
        - synonyms made against a relationship() can
          be passed to query.join(), options sent
          to query.options(), passed by name
          to query.with_parent().
- revised the approach taken earlier to just
propagate "property" out from the proxied attr the same
way queryable attribute does.