called without necessarily aborting the current transaction. This is
required by things like the resolve_url machinery, where there is a
need to call the exception() method to get a meaningful error. The
resolve_url method in HTTPRequest.Request has been changed to take
advantage of this. The existing semantics of RESPONSE.exception()
are unchanged - it will automatically abort just as it did before
unless you pass the keyword arg abort=0 when calling the method.