Create a request object for the specified method and url.

def _make_req(self, method, url, methname, headers=None):
        """Create a request object for the specified method and url."""

        # Build up headers
        hset = hdrs.HeaderDict()

        # Walk through our global headers
        for hdr, value in self._headers.items():
            # If it's a callable, call it
            if callable(value):
                value = value(methname)
            else:
                # OK, just stringify it
                value = str(value)

            # If it's meaningful, attach it
            if value:
                hset[hdr] = value

        # Were headers passed in?
        if headers is not None:
            # Update from specified headers
            hset.update(headers)

        # Hook method to instantiate requests
        self._debug("Creating request %s.%s(%r, %r, headers=%r)",
                    self._req_class.__module__, self._req_class.__name__,
                    method, url, hset)
        return self._req_class(method, url, self._client, self._procstack,
                               headers=hset, debug=self._debug)