Rename ObjectClassRefType.

[Gary P Cole <Gary.P.Cole@Sun.COM>]

I finally thought of a better name for ObjectClassRefType.  I think we 
should call it SchemaEntityRefType since that's more generic (in that it 
is less specific to DSML).
- Each element of this type refers to an "objectClass" when the target 
schema is DSML,
  but refers to a top-level element when the target schema is generic 
XML Schema.
- It is easier to define a term like "schema entity" in the 
specification than it is
   to overcome the connotations of a term as popular as "objectclass".