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
```
For the following code:
```rustc
struct Bar;
struct Bar;
fn main () {
}
```
show
```nocode
error[E0428]: a type named `Bar` has already been defined in this module
--> src/test/compile-fail/E0428.rs:12:1
|
11 | struct Bar;
| ----------- previous definition of `Bar` here
12 | struct Bar;
| ^^^^^^^^^^^
error: aborting due to previous error
```
instead of
```nocode
error[E0428]: a type named `Bar` has already been defined in this module
--> src/test/compile-fail/E0428.rs:12:1
|
11 | struct Bar;
| ----------- previous definition of `Bar` here
12 | struct Bar;
| ^^^^^^^^^^^
error[E0428]: a value named `Bar` has already been defined in this module
--> src/test/compile-fail/E0428.rs:12:1
|
11 | struct Bar;
| ----------- previous definition of `Bar` here
12 | struct Bar;
| ^^^^^^^^^^^
error: aborting due to 2 previous errors
```
