Fix up for refactor_funcall
Implement template overload set with basic test cases
fix Issue 1900 - Template overload sets & traits templates
fix Issue 7780 - Template mixin'd members do not properly overload
fix Issue 8352 - Wrong "__overloadset isn't a template" error
fix Issue 8441 - mixin containing template functions causes compiler errors
fix Issue 9235 - Template mixin doesn't allow to mixin non-conflicting overloads