auto merge of #4575 : mttr/servo/warnings, r=jdm

Notes:

* This adds `#![allow(missing_copy_implementations)]` to components/*/lib.rs. I'm not sure how to approach the missing Copy warnings (are there things for which Copy should NOT be implemented, and how can I tell?) so I stuck this in to make life easier when looking through the warnings. I can easily remove this if necessary. 
* This leaves the following type of warnings, which I couldn't figure out how to approach (I'll investigate it later if no one else wants to).
```
css/matching.rs:72:23: 72:35 warning: use of deprecated item: Use overloaded core::cmp::PartialEq, #[warn(deprecated)] on by default
css/matching.rs:72         this_as_query.equiv(other)
                                         ^~~~~~~~~~~~
css/matching.rs:95:10: 95:49 warning: use of deprecated item: Use overloaded core::cmp::PartialEq, #[warn(deprecated)] on by default
css/matching.rs:95 impl<'a> Equiv<ApplicableDeclarationsCacheEntry> for ApplicableDeclarationsCacheQuery<'a> {
```

1 files changed, 1 insertions, 1 deletions

diff --git a/components/script/dom/htmlformelement.rs b/components/script/dom/htmlformelement.rs
index 33313116161..fc8f9879c7b 100644
--- a/components/script/dom/htmlformelement.rs
+++ b/components/script/dom/htmlformelement.rs
@@ -246,7 +246,7 @@ impl<'a> HTMLFormElementHelpers for JSRef<'a, HTMLFormElement> {
         let node: JSRef<Node> = NodeCast::from_ref(self);
         // TODO: This is an incorrect way of getting controls owned
         //       by the form, but good enough until html5ever lands
-        let mut data_set = node.traverse_preorder().filter_map(|child| {
+        let data_set = node.traverse_preorder().filter_map(|child| {
             if child.get_disabled_state() {
                 return None;
             }