- We no longer attach __content_type__ or any interfaces to
  factories or constructed content.  Instead, we attach, if necessary,
  a __factory_type__ attribute and use the factory type as a key
  into the content registry to find out information about the content
  object (e.g. is it propertied?  is it catalogable?).  We only
  use a wrapper to attach __factory_type__ if the object is not a class or
  if an explicit ``factory_type`` argument is supplied to add_content_type.

- The IContent interface has been removed.  Objects which have a factory
  type in the content registry are "content", that's the only definition
  we require.

- Replace IPropertied interface with is_propertied content
  registry getter.  IPropertied interface no longer exists.

- Replace ICatalogable interface with is_catalogable content
  registry getter.  ICatalogable interface no longer exists.

- The substanced.content.set_content_type function has been removed.

- The substanced.content.get_content_type function now operates
  by attempting to divine the content type from the factory
  type attached to the object (if any, defaulting to dotted name
  of the object's class).

- A new substanced.content.get_factory_type function now exists.

- The add method of the ContentRegistry now must be passed a factory
  type as well as a content type and a factory.

- The implementation of the ContentRegistry now maps factory types
  to content types, and uses in various places the factory type of
  an object to compute its content type.

- The get_meta_interfaces function in substanced.content has been removed.
  Interfaces are no longer used to signify catalogability or propertysheetness
  nor does the use of an interface as a content type imply that the
  content object implements that interface.

- The ``interfaces`` argument to @content (or add_content_type) no longer
  means anything special.  The supplied interfaces are no longer attached
  to the decorated factory.

- Catalog content type is now 'Catalog' instead of ICatalog.  The ICatalog
  interface continues to exist, and the Catalog class still implements it.

- File content type is now 'File' instead of IFile.  The IFile interface
  continues to exist and the File class still implements it.

- Folder content type is now 'Folder' instead of IFolder.  The IFolder interface
  continues to exist and the Folder class still implements it.

- Site content type is now 'Site' instead of ISite.  The ISite interface
  continues to exist and the Site class still implements it.

- ObjectMap content type is now 'Object Map' instead of IObjectMap.  The
  IObjectMap interface continues to exist and the ObjectMap class still
  implements it.

- Principals content type is now 'Principals' instead of IPrincipals.  The
  IPrincipals interface still exists and the Principals class still implements
  it.

- Users content type is now 'Users' instead of IUsers.  The IUsers class still
  exists and the Users class still implements it.

- Groups content type is now 'Groups' instead of IGroups.  The IGroups class
  still exists and the Groups class still implements it.

- Group content type is now 'Group' instead of IGroup.  The IGroup class
  still eixsts and the Group class still implements it.

- User content type is now 'User' instead of IUser.  The IUser class still
  exists and the User class still implements it.

- PasswordResets content type is now 'Password Resets'.  The IPasswordResets
  class still exists and the PasswordResets class still implements it.

- PasswordReset content type is now 'Password Reset'.  The IPasswordResets
  interface still exists and the PasswordReset class still implements it.

- The properties management view now uses the "propertied" predicate
  rather than context=IPropertied.

- Add 'catalogable' view predicate (CatalogablePredicate).

- Add 'propertied' view predicate (PropertiedPredicate).

- Fix bug in add_mgmt_view where default value for xhr was False instead
  of None.

- Rename **other_predicates anonymous keyword accepter to **predicates
  (as per latest Pyramid trunk).

- Fix bug in add_mgmt_view where predicate list was mutated in-place
  instead of copied first (predicate introspection mismatches would have
  resulted).

- Simplified implementation of @mgmt_view decorator.

- Object events now have a 'registry' attribute.

- Adjust blog demo for new regime.
Merge branch 'master' into feature.avoidglobalmutation
Merge branch 'feature.avoidglobalmutation'