MOF24 — Move operations from 9.1 Element to 9.3 Object: equals, get/set/unset/isSet

As currently specified in 9.1, it makes sense to have these operations available in Object, not Element.
Pete concurred with me on making this change in MOF2.4; he said that these operations may have been shuffled at the last minute during MOF2.0 finalization.

Move the operations in the metamodel & the specification as indicated in the summary.
The specification of get/set operations should be in terms of ReflectiveCollection instead of ReflectiveSequence since the characteristics of a property with upper bound greater than 1 could be that of a sequence, bag, set or ordered set as specified in UML2.4 (see Superstructure clause 7.3.45, table “Collection types for properties”). Adding support for all of the collection types in UML is a separate issue.