Don't ICE if an argument in a default method doesn't have a name. Closes #8417.
Add `self` to the ast_map for provided methods. Closes #8010.
Fix type parameter handling for static default methods. Closes #8654.
Substitute into the impl method rather than the trait method when emitting vtables. Closes #8601.
Don't do a bogus substitution on the transformed self ty for objects. Closes #8664.
auto merge of #8659 : msullivan/rust/default-methods, r=graydon