Revert "Changing `client.request()` to return the XHR Object such that it can be aborted, etc."

This reverts commit a50c98f152a05a8e8cd452f0aac105ea2856ecbf.
Decorating the `Deferred` returned from `client.request()` with the `XMLHttpRequest` instance as an `xhr` property
Merge pull request #441 from avoidwork/edge

Reverting an erroneous change to `client.request()`