Allow callers to specify to NSM that we're in a non-interactive context

(nsm-noninteractive): New variable to enable callers to say that
we're running in a non-interactive context.
Introduce a new `url-request-noninteractive' interface variable

* etc/NEWS: Mention `url-request-noninteractive'.

* lisp/url/url-http.el (url-http-noninteractive): New local variable.
(url-http): Set it locally.

* lisp/url/url-queue.el (url-queue-start-retrieve): Mark all we do as
noninteractive.

* lisp/url/url-vars.el (url-request-noninteractive): New interface variable.
* net/nsm.el (nsm-security-level): Fix defcustom.
* url-http.el (url-http): Protect against `url-http-noninteractive' being unbound.
* gnutls.c (gnutls_certificate_details): Fix comment.
* gnutls.c: Cargo-cult implementation of the Windows gnutls interface functions.
NSM certificate display fix

* net/nsm.el (nsm-format-certificate): Protect against not all
identifiers having all parts.