Adding Intel XHR timeout tests.

Signed-off-by: Dominik Röttsches <dominik.rottsches@intel.com>
Review comments addressed.

> I'd prefer if the code that matters for the test was in the file that "is" the test itself. (In this case that might mean some more code duplication, so I guess it's a YMMV thing.) I assume much of the same effect could be achieved by putting the essential code for each test in a .js file and linking it to the main file either with a SCRIPT src=.. or a Worker.

Refactored so that test definitions are in individual .js files and imported for document and worker case. Simplified individual test files from an onload method to a bottom-of-page inline script. Simplified launch process so that no postMessage() is necessary.

> PS AbortedRequest.prototype.startXHR() method doesn't need both a "me" and a "_this" variable.--

Removed me var.

Added missing *-overrides.html files.

A running demo of these tests can be found here: http://w3ctests.roettsch.es/XMLHttpRequest/
Merge pull request #1 from drott/feedbackFromHallvors

Incorporating feedback from Hallvord