* url-http-ntlm.el: Require cl-lib.
(url-http-ntlm--ensure-keepalive): Use cl-assert.
(url-http-ntlm--get-stage): Use cl-destructuring-bind.
(url-http-ntlm--authorisation): Use cl-second.
(url-http-ntlm--rmssoc): Use cl-remove.
(url-ntlm-auth): Use cl-case and cl-destructuring-bind.