fix for issue #9394

This solves problem of incorrect indexing into vtable
when method from super trait was called through pointer
to derived trait.
Problem was that offset of super trait vtables
was not calculated at all.
Now it works, correct offset is calculated by
traversing all super traits up to super trait
where method belongs. That is how it is
intended to work.
Merge branch 'master' of https://github.com/bmaxa/rust