Removed custom error message for unresolved references to connection
ends.  A more detailed message will be provided by the validator.
findAccessConnectionEnd was looking for elements of PortConnectionEnd
when the context is a SubprogramCall.  Changed this to
AccessConnectionEnd.
Check that the source and destination of an access connection are
Subcomponents before casting them.  A ClassCastException was ocurring
when the connection end was a SubprogramProxy.
When checking the source and destination categories of access
connections, consider SubprogramProxy to be of category Subprogram.
Also, do not report an error if the source or destination could not be
resolved or if they are of a type other than AccessConnectionEnd.  In
those cases, an error is already reported.
Don't check the classifiers of parameter connection ends if the ends are
unresolved or not instances of ParameterConnectionEnd.
When checking port connection classifiers, place the warning on the
source or the destination instead of the whole connection.
When checking the source and destination directions of a port
connection, do not report an error if the source or destination could
not be resolved or if they are of a type other than PortConnectionEnd.
In those cases, an error is already reported.
When linking a Context for ConnectedElements, don't perform a type check
based upon the connection type.  Link any Context object and let the
validator give an error.
When linking a ConnectionEnd for ConnectedElements, don't perform a type
check based upon the connection type.  Link any ConnectionEnd object and
let the validator give an error.
Report some connection errors on the source or destination only instead
of the whole connection.
When checking the classifiers of access connection ends, retrieve the
classifier from a SubprogramProxy.
Report some connection errors on the source or destination only instead
of the whole connection.
Report some connection errors on the source or destination only instead
of the whole connection.
When checking port connection ends, only check if both ends are
instances of PortConnectionEnd.
Moved the type checking for the ends of an AccessConnection from the
linker to the validator.
Moved the type checking for the ends of a FeatureConnection from the
linker to the validator.
Moved the type checking for the ends of a FeatureGroupConnection from
the linker to the validator.
Moved the type checking for the ends of a ParameterConnection from
the linker to the validator.
Moved the type checking for the ends of a PortConnection from
the linker to the validator.
Changed the scope for ConnectedElement's context reference to match the
changes to the linker.  Allow all visible Context object to be in the
scope, not just the Context objects appropriate for the current
connection type.