[osis-core] Since we may be releasing osisCore.1.1.2.xsd should we consider making the schema extensable.

[Todd Tillinghast]

Patrick,

When I tried to create a schema that extends from osisCore.1.1.1.xsd, I
was unable to because almost all of the Simple and Complex types are
created "inline".  If we were to create the Simple and Complex types
used in the schema as named types then we could extend the schema.  

None of this could change the meaning or behavior of the schema, but
would leave room for opportunities in the future to provide new
specialized behavior while leaving the core schema unchanged.  

Todd