Isolate why the XHR request tests are failing.
Make XHR a module. No more shared global state.

This change requires updates of a network.js and a few tests to handle the new way of creating/starting the XHR module.
Move xhr.js into modules since it is now a module & other cleanup.
fix the jshint error
Fix the way arguments are sliced to appease IE8
Updating with @6a68's suggestions.

* Move the magic XHR delay number to browserid.js->XHR_DELAY_MS
* Rename getRequest to getRequestInfo
* Re-include testmob.org in the tests
Merge pull request #3655 from shane-tomlinson/issue_3647_async_requests

Issue 3647 async requests

@6a68 gave the r+ if concerns were met. Concerns addressed. Merging. Going to open a new PR to get context out of xhr.js and into network.js.