Fix method searching to always ignore methods overridden by subclasses.

Previously, they were only being ignored if they were 'found' as part of the search.
Fix implicit enum coercing to respect existing overloads.
Fix case of DuplicationStrategy enum, relying on DSL type coercion to allow user to specify value as lower case string.

This implies exposing enhanced objects as part of the CopySpec DSL. At this point, this is not comprehensive. That is coming in a subsequent commits.
Enhance the copy specs exposed by Project.copySpec() and Project.copy().
Enhance all the objects that copy specs and tasks expose to the user.