The routine to determine if a "Link" sub-menu entry is valid.
We give an implementation, rather than declaring as abstract, so a
sub-class that disables the "Link" menu need not provide an
implementation.
Deprecated.ExtensionMechanismsFactory::isStereotype should be used
instead. Since this should only ever be used together with predefined
stereotypes the base class can be found in the UML 1.3 specification.
Returns true if the given stereotype has a baseclass that equals the baseclass
of the given modelelement or one of the superclasses of the given modelelement.