Clearer Error Message for Duplicate Definition

Clearer use of the error message and span labels to communicate
duplicaiton defitions/imports.

New error format:

```
error[E0428]: the name `Foo` is defined twice
 --> example.rs:2:1
  |
1 | trait Foo { }
  | ------------- previous definition of the trait `Foo` here
2 | struct Foo { }
  | ^^^^^^^^^^^^^^ `Foo` redefined here
  = note: `Foo` must be defined only once in the type namespace of this module

error: aborting due to previous error
```

1 files changed, 4 insertions, 3 deletions

diff --git a/src/test/compile-fail/enum-and-module-in-same-scope.rs b/src/test/compile-fail/enum-and-module-in-same-scope.rs
index 527ac7505a6..59b4d715c2d 100644
--- a/src/test/compile-fail/enum-and-module-in-same-scope.rs
+++ b/src/test/compile-fail/enum-and-module-in-same-scope.rs
@@ -8,12 +8,13 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-enum Foo { //~ NOTE previous definition of `Foo` here
+enum Foo { //~ NOTE previous definition of the type `Foo` here
     X
 }
 
-mod Foo { //~ ERROR a type named `Foo` has already been defined
-          //~| NOTE already defined
+mod Foo { //~ ERROR the name `Foo` is defined multiple times
+          //~| NOTE `Foo` redefined here
+          //~| NOTE `Foo` must be defined only once in the type namespace of this module
     pub static X: isize = 42;
     fn f() { f() } // Check that this does not result in a resolution error
 }