don't change readystate if it's already been changed
Remove not-yet-implemented APIs, and update MouseEvent to specification.
Remove low-level pointer stitching methods from Node.

There is no good reason for the additional abstraction here.

This commit also adds assertions that were suggested in XXX comments.
Add a static from_rooted method to JS<T> #2309
auto merge of #2548 : ebalint/servo/master, r=Ms2ger
auto merge of #2527 : Manishearth/servo/xhr-wpt-ready-state, r=Ms2ger

For the wpt test [open-open-send.htm](https://github.com/w3c/web-platform-tests/blob/master/XMLHttpRequest/open-open-send.htm)


Blocks #2525
Remove tests for unimplemented features.
auto merge of #2545 : Ms2ger/servo/nyi, r=jdm
auto merge of #2546 : Ms2ger/servo/node-pointer-stitching, r=jdm

There is no good reason for the additional abstraction here.

This commit also adds assertions that were suggested in XXX comments.
auto merge of #2547 : Ms2ger/servo/dictionary-tests, r=jdm
Return the default value from getJSToNativeConversionTemplate, to allow reusing it more easily.

This commit does not change the generated code.
Rewrite the dictionary codegen to use pattern matching rather than is_some/unwrap.
Support dictionary members without default values.