HTMLImageElement attribute getters and setters
Remove the return value from DefineDOMInterface.

This moves the assertion from its only caller into the function itself, to
clarify that we don't intent to deal with any failure here.
Remove unused variable 'obj' from binding functions.

This removes the local variable and prefixes the argument with an underscore.
Neither is used right now.
auto merge of #2113 : Ms2ger/servo/DefineDOMInterface, r=jdm

This moves the assertion from its only caller into the function itself, to
clarify that we don't intent to deal with any failure here.
auto merge of #2114 : Ms2ger/servo/unused-obj-local-arg, r=jdm

This removes the local variable and prefixes the argument with an underscore.
Neither is used right now.
auto merge of #2054 : sankha93/servo/imageattr, r=jdm
Implement FromJSValConvertible for JS<T>.
box_: Remove unused code that resurfaced with the Rust upgrade
auto merge of #2119 : pcwalton/servo/rm-unused-code, r=pcwalton

trivial
auto merge of #2112 : Ms2ger/servo/IDLInterface-JS, r=jdm