require_oauth decorator was always succeeding.

verify_request() returns a tuple of (valid, oauth_request). The code was
treating it as if it returned just a bool, and since the never-empty
tuple was always truthy, requests always seemed to work.

Fixes ib-lundgren/flask-oauthprovider/#3
Instead of returning response objects, raise errors.

Some wrapping decorators (like mimerender) expect dicts, not response
objects.

Raising exceptions for HTTP error responses avoids quirks of the
applicaitons. (This is also what flask.abort() eventually does).
Merge pull request #1 from datalogics-kam/fixes-for-dl

* datalogics-kam/fixes-for-dl:
  Instead of returning response objects, raise errors.
  require_oauth decorator was always succeeding.