Kill off a long-hated Camel kludge: "empty" URLs and

	Kill off a long-hated Camel kludge: "empty" URLs and
	query_auth_types_generic.

	* camel-url.c: Remove "empty" from CamelURL.
	(camel_url_new): No longer set it.
	(camel_url_to_string): Treat "" as equivalent to NULL for
	authmech. (Unrelated change, but it simplifies some stuff with the
	new config dialog.)

	* camel-service.c (camel_service_new): Remove url->empty check: if
	the URL isn't valid, we don't create the service.
	(camel_service_query_auth_types): No longer need to switch between
	generic and connected variants.

	* providers/smtp/camel-smtp-transport.c (query_auth_types):
	* providers/pop3/camel-pop3-store.c (query_auth_types):
	* providers/nntp/camel-nntp-store.c (nntp_store_query_auth_types):
	* providers/imap/camel-imap-store.c (query_auth_types):
	* camel-remote-store.c (remote_query_auth_types): Remove generic
	version, rename connected version.