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.
Enable some more dictionary codegen tests.
Support enumerations in dictionaries.
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
Add an option to set device pixel ratio
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.
Default to 1 dppx in headless mode
auto merge of #2547 : Ms2ger/servo/dictionary-tests, r=jdm
Rename BindingDeclarations to Bindings.
auto merge of #2551 : Ms2ger/servo/bindings-rename, r=jdm
Remove needless '&mut self' from element.rs.
Remove needless 'self' mutability from DocumentTypeMethods::Remove().
Remove needless 'self' mutability from CharacterDataMethods::Remove().
auto merge of #2552 : saneyuki/servo/mut, r=jdm

related #2514
auto merge of #2549 : mbrubeck/servo/hidpi-opt, r=metajack

This is part of the fix for #2276. r? @metajack