Fixes for browser compatibility, adding hooks to testmob or unit tests.

* Hook up unit tests to testmob
* Add function.prototype.bind for browsers that do not have it.
* Remove the "Close" header, this is not supposed to be written to.
* General cleanup
Immediately return the mock XHR object on calling ajax.
Replace function.prototype.bind with curry
Changing the type of error returned from the server from 500 to 400.  Chrome on Windows sometimes has problems with 500s
* Add the ability to abort a request.
* Add the ability to set headers on a request.