A different approach is taken for supporting casting smart pointers up the
inheritance hierarchy. We no longer try to replace the underlying pointer type,
provided in the 'feature:smartptr', with the base class type. Such as morphing
'std::shared_ptr<(Derived)>' into 'std::shared_ptr<(Base)>'. Instead, we simply
use 'feature:smartptr' from the base class. This is more reliable than trying to
pattern match the pointer type in the feature. The base class must of course
also have the 'feature:smartptr' set, and this is still checked for as before.
The feature is now parsed in one place and stored in the parse tree in the
new 'smart' attribute for handling by the target languages.
Fix also improves the handling of the type parsed in 'feature:smartptr' in that
the type is now normalized and resolved in the scope of the class it is attached
to.
Closes#2768
William S Fulton