Use new attributes syntax in properties.rs
auto merge of #2279 : Manishearth/servo/patch-3, r=jdm
Change some isString() checks in the WebIDL parser to isDOMString() checks.
Add missing ByteString support in the WebIDL parser.
Change some isString() checks in the WebIDL codegen to isDOMString() checks.
Implement WebIDL codegen for ByteString.
auto merge of #2286 : Ms2ger/servo/ByteString, r=jdm