Allow union types to be used as return values
auto merge of #2573 : Manishearth/servo/union-return, r=Ms2ger

Blocks #2559
Make the bindings make target work on all platforms.
auto merge of #2614 : saneyuki/servo/make, r=jdm

Fix #2583
Use RefCell for mutability of Element::style_attribute.
auto merge of #2615 : saneyuki/servo/refcell, r=Ms2ger

related: #2513
Support for extension methods, getResponseHeader(), and an extra error
Make sync requests not crash / remove associated leak
Empty methods are not allowed
auto merge of #2613 : Manishearth/servo/xhr-wpt-methods, r=Ms2ger

For [XMLHttpRequest/open-method-case-sensitive.htm](https://github.com/w3c/web-platform-tests/blob/master/XMLHttpRequest/open-method-case-sensitive.htm), [XMLHttpRequest/XMLHttpRequest/open-method-insecure.htm](https://github.com/w3c/web-platform-tests/blob/master/XMLHttpRequest/open-method-insecure.htm), [XMLHttpRequest/XMLHttpRequest/open-method-responsetype-set-sync.htm ](https://github.com/w3c/web-platform-tests/blob/master/XMLHttpRequest/open-method-responsetype-set-sync.htm) in particular. `getResponseHeader()` is used by a lot of other tests (the harness echoes most of the metadata in the response headers, which is tested on this side) 

The sync changes fixes half of the timeouts to give meaningful results.



Blocks #2525
Fix some deprecated warnings for to_owned()
auto merge of #2617 : Manishearth/servo/string-warn, r=Ms2ger
Support GlobalEventHandlers.onclick.
auto merge of #2619 : Ms2ger/servo/onclick, r=jdm
Remove PaddedUnsafeFlow.
Fix type the type name.
Remove 'LayoutNode.pad' field.