False positive in match blocks for shadow

[Manishearth]

match (1,1,2) {
(a,b,2) | (2,a,b) => (),
_=>()
}

There's no shadowing here.

test.rs:7:14: 7:15 warning: a is shadowed by 1 [-W shadow-unrelated]
test.rs:7 (a,b,2) | (2,a,b) => (),
                       ^
test.rs:6:10: 6:11 note: initialization happens here
test.rs:6 match (1,1,2) {
                   ^
test.rs:7:14: 7:15 help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated
test.rs:7:16: 7:17 warning: b is shadowed by 2 [-W shadow-unrelated]
test.rs:7 (a,b,2) | (2,a,b) => (),
                         ^
test.rs:6:12: 6:13 note: initialization happens here
test.rs:6 match (1,1,2) {
                     ^
test.rs:7:16: 7:17 help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated

Fixing #318 would make it easier to fix this.