adding test for calling open() to terminate the abort() algorithm

Two tests based on comments here:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=27033
open-during-abort-event calls open() from an upload.abort event listener. abort() is called from the xhr.loadstart event. Note that Webkit-based browsers do not currently fire abort events here. Per the spec, they should. Firefox fails this test too, because it (tentatively) asserts that open() in xhr.upload.onabort should terminate abort processing so that xhr.onabort should not fire.

open-during-abort-processing calls open() from a readystatechange fired due to an abort() call.