evaluate assertions at appropriate time

Evaluate assertions at appropriate time in XMLHttpRequest/abort-event-order.html, to compliment
10010b1's corrected expected results

Closes #958
assert readyState updated after abort() in nextTick

Per the spec, the readyState is updated after the events are dispatched. Since the
assertion occurs during the final loadend event handler, there must be a pause before
the readyState can be tested, as browsers behaving according to the spec will not
have updated the readyState yet.
tests for chapter 'Extensions to Document Interface'
New test: send sync blocks async
removing test mistakenly comitted directly to master
improving tests according to Dominic's notes
Merge pull request #959 from caitp/issue-958

evaluate assertions at appropriate time
evaluate assertions immediately after xhr.abort()

Anne has made a good point that it's more appropriate to perform assertions here, rather than in
one of the other event listeners, because XMLHttpRequest#abort() should be synchronous, and the
abort and loadend events are dispatched synchronously.

So, this simplifies the test and avoids relying on setTimeout(), which is nice, and potentially
avoids missing assertions in non-compliant browsers.
Merge pull request #961 from sgrekhov/submission/unipro-custom-elements-12

tests for chapter 'Extensions to Document Interface'
Merge pull request #968 from caitp/xhr-abort-events-noncompliance

evaluate assertions immediately after xhr.abort()