These are all really SoupContext functions, so move them to soup-context.c

These are all really SoupContext functions, so move them to soup-context.c

	* libsoup/soup-auth.c (soup_auth_lookup, soup_auth_set_context,
	soup_auth_invalidate): These are all really SoupContext functions,
	so move them to soup-context.c (and rename them appropriately).
	(soup_auth_get_protection_space): New method to get the
	"protection space" of an auth (paths where it is valid).
	(soup_auth_invalidate): New method to try to un-authenticate an
	auth (so we can keep the domain info cached even if the auth info
	is wrong).
	(basic_pspace_func): Basic protection space is all directories
	below the current one.
	(basic_invalidate_func): Clear the encoded username/password
	(digest_pspace_func): Digest protection space is either the whole
	server, or "what the domain parameter says" (though we don't deal
	with cross-host domains).
	(digest_invalidate_func): Return FALSE; bad digest auth info isn't
	cacheable.
	(digest_parse_func, digest_free): Set/free domain parameter
	(ntlm_pspace): NTLM protection space is always the whole server.
	(ntlm_invalidate): Clear the auth state.
	(soup_auth_new_ntlm): Make this non-static
	(SoupAuth): Replace the quad-state "status" field with an
	"authenticated" boolean.

	* libsoup/soup-private.h (SoupHost): Replace the "valid_auths"
	hash with separate "auth_realms" (path->realm) and "auths"
	(realm->auth) hashes. Also add a "use_ntlm" flag.

	* libsoup/soup-context.c (soup_context_unref): Update SoupHost
	freeing code.
	(connection_free): Don't the connection's auth, just free it.
	(soup_context_lookup_auth): Formerly soup_auth_lookup, but now
	does two-stage lookup (path->realm then realm->auth) and also
	deals with NTLM hacks.
	(soup_context_update_auth): Mostly formerly soup_auth_set_context,
	but also large parts of authorize_handler. Updates the auth hashes
	based on information from a 401 or 407 response. Does a better job
	than authorize_handler did of not throwing away good information.
	(soup_context_preauthenticate): New; fakes up auth info so that
	requests will end up using authentication without the server
	needing to return an error first.
	(soup_context_authenticate_auth): Moved out of authorize_handler
	so it can be used at request-sending time too, if we know that we
	need it. (That way we can avoid requeuing the request if it isn't
	going to be able to be authenticated.)
	(soup_context_invalidate_auth): Sort of like the old
	soup_auth_invalidate, but only destroys the auth data, while still
	remembering the path->realm mapping.

	* libsoup/soup-message.c (authorize_handler): Mostly moved into
	soup_context_update_auth.
	(maybe_validate_auth): Remove this; it was only useful because of
	bugs elsewhere in the auth handling.

	* libsoup/soup-queue.c (soup_encode_http_auth): Update for
	soup_context_lookup_auth. If the returned auth isn't
	authenticated, call soup_context_authenticate_auth() on it.

	* tests/auth-test.c: New (from soup-refactoring branch). Tests
	that the Basic/Digest auth code does the right thing. (TODO: find
	a good way to add NTLM tests too.)

	* tests/Makefile.am (check_PROGRAMS): add auth-test