…anxiyn

I was able to remove unused imports, and fix the following warnings

src/libstd/hashmap.rs:23:15: 23:23 warning: unused import [-W unused-imports (default)]
src/libstd/task/spawn.rs:95:15: 95:23 warning: unused import [-W unused-imports (default)]
src/libstd/rt/uv/mod.rs:42:0: 42:9 warning: unused import [-W unused-imports (default)]
src/libstd/rt/uv/mod.rs:45:0: 45:9 warning: unused import [-W unused-imports (default)]
src/librustc/middle/trans/meth.rs:26:0: 26:26 warning: unused import [-W unused-imports (default)]
src/librustc/back/link.rs:210:20: 210:25 warning: unused import [-W unused-imports (default)]

I was unable to fix the following unused import warnings. The code
here was weird.

src/libextra/std.rc:40:11: 40:14 warning: unused import [-W unused-imports (default)]
src/libextra/std.rc:40:16: 40:24 warning: unused import [-W unused-imports (default)]

fix `needless_borrow` suggestion

fixes: rust-lang#2610

While I'm working on this, should needless_borrow be split into two? One lint for expressions and another for patterns. In expression it only lints when the compiler inserts a dereference, but for patterns it's whenever a double reference is created. I think at least the case where a double reference is needed should be split into a new lint as it's not 'needless', it can just be done without a ref binding.

For illustration:

```rust
fn foo(x: &&str) {}

match Some("test") {
    // ref binding is useless here
    Some(ref x) => *x,
    _ => (),
}

match Some("test") {
    // ref binding is useless here
    Some(ref x) => x.len(),
    _ => (),
}

match Some("test") {
    // double reference is needed, but could be `Some(x) => foo(&x)`
    Some(ref x) => foo(x),
    _ => (),
}
```

changelog: Improve the suggestion for `needless_borrow` in patterns to change all usage sites as needed.
changelog: Add lint `ref_binding_to_reference`

Move `needless_borrow` to style

fixes: rust-lang#3742

rust-lang#7105 should be merged first to fix the false positive.

changelog: move `needless_borrow` from `nursery` to `style`