Allow http client to add and revoke certificates.

Allow http client to add and revoke certificates.

	* client-http.cxx (http_client_backend::fill_in_server_info): Add cert
	   awareness for cert add/revoke.
	  (http_client_backend::trust_server_info): New for cert add.
	* nss-server-info.cxx (add_server_trust): Just pass on http server
	   names.
	  (nss_get_specified_server_info): Likewise.
	* nsscommon.cxx (add_client_cert): Check if nss is already setup.
	  Add init_db parameter.  Callers updated.
	* testsuite/lib/http_server.exp (http_start_server): Add server trust.
	  (http_shutdown_server): Revoke server trust.