allow to process post vars in DELETE requests

Our use case for requiring post_vars variables in a DELETE is that we wanted
our interface to support a bulk deleting method so as to reduce the number of
requests needed to be made.

As part of our miration path of getting our app to speak JSON from end-to-end,
we also wanted to ensure it was able to take a message body similar to a web
form submission.

e.g.
[form data]
    DELETE /app/rest/categoryofobjects HTTP/1.1
    ...
    Content-Type: application/x-www-form-urlencoded
    Content-Length: ...

    ids=1&ids=2ids=3...

[JSON]
    DELETE /app/rest/categoryofobjects HTTP/1.1
    ...
    Content-Type: application/json
    Content-Length: ...

    {
        "ids": [1, 2, 3, ...]
    }

NOTE: the spec is fuzzy on this point, but we feel that this change doesn't actually hurt anything so is worthy of inclusion for flexibility-sake