E0260 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0260.rs

E0260 needs a span_label, updating it from:

error[E0260]: an extern crate named `collections` has already been imported in this module
  --> src/test/compile-fail/E0260.rs:13:1
   |
11 | extern crate collections;
   | ------------------------- previous import of `collections` here
12 | 
13 | mod collections { //~ ERROR E0260
   | ^

To:

error[E0260]: an extern crate named `collections` has already been imported in this module
  --> src/test/compile-fail/E0260.rs:13:1
   |
11 | extern crate collections;
   | ------------------------- previous import of `collections` here
12 | 
13 | mod collections { //~ ERROR E0260
   | ^ `collections` already imported

Bonus: Underline the name of the conflicting definition, if possible:

error[E0260]: an extern crate named `collections` has already been imported in this module
  --> src/test/compile-fail/E0260.rs:13:1
   |
11 | extern crate collections;
   | ------------------------- previous import of `collections` here
12 | 
13 | mod collections { //~ ERROR E0260
   |     ^^^^^^^^^^^ already imported

[creativcoder]

I'd like to work on this.

[sophiajt]

@creativcoder - looks like @EugeneGonzalez claimed this one, but feel free to look at the list as there are some open ones no one has claimed

[creativcoder]

Sure. I'll go have a look.

[sophiajt]

@creativcoder - I'm releasing this one so someone else can volunteer since it's gone 15 days without a fix, but there are other error codes you can sign up for if you want to fix more.