unhelpful "expected T, found T" message for identically named but distinct type parameters

[ben0x539]

struct Thing<T> {
    thing: T
}   

impl<T> Thing<T> {
  fn get<T>(self) -> T { 
    self.thing
  }   
}   

foo.rs:7:4: 7:14 error: mismatched types: expected `T` but found `T` (expected type parameter but found type parameter)
foo.rs:7     self.thing
             ^~~~~~~~~~

It's all right and proper but maybe we could come up with a way to denote that those two T come from different type parameter lists, or even ban type parameters shadowing each other.

[ghost]

Closing as a dupe of #3404.