Removed ManyToMany::Proxy (to be rebuilt)
Removed ManyToMany::Proxy (to be rebuilt)

* Removed RelationshipChain (should not be rebuilt)
* Updated OneToMany::Proxy to be a subclass of Collection
* Updated the Postgres typemap to use the real type name rather than the alias
* Updated has() and belongs_to() to throw an exception of the :through
  option is provided.  This is just until many to many associations are
  rewritten.
* Added Collection#save.  Moved from OneToMany::Proxy#save

datamapper/dm-postgres-adapter