Fix make_mono_id to take into account self types. Closes #7536.
Make privacy checking on default methods for cross crate structs not fail. Closes #7481.

It is unclear to me that the way method call privacy checking is done
makes any sense, though. It is only performed if the type is a
struct...
auto merge of #7545 : msullivan/rust/default-methods, r=catamorphism

r?