Add "authenticate" and "reauthenticate" signals. (invalidate_auth): Remove

Add "authenticate" and "reauthenticate" signals. (invalidate_auth): Remove

	* libsoup/soup-session.c: Add "authenticate" and "reauthenticate"
	signals.
	(invalidate_auth): Remove the call to soup_auth_invalidate.
	(authenticate_auth): soup_auth_fn is gone. If the URI doesn't
	contain authentication, then emit "authenticate" or
	"reauthenticate" (depending on whether or not this is the first
	time we've asked for a password for this auth).
	(update_auth_internal): If the server rejects our
	username/password, don't bail out immediately. Try doing a
	"reauthenticate" first.

	* libsoup/soup-misc.c (soup_set_authorize_callback): Gone

	* libsoup/soup-auth.c (soup_auth_new_from_header_list): Remove the
	"pref" arg.
	(soup_auth_invalidate): Remove this; it doesn't actually do
	anything useful for us.

	* libsoup/soup-auth-basic.c (invalidate): Remove
	* libsoup/soup-auth-digest.c: (invalidate): Remove
	* libsoup/soup-auth-ntlm.c: (invalidate): Remove

	* libsoup/soup-uri.c: Remove all references to "authmech".
	(soup_uri_set_auth): Remove this too.

	* tests/auth-test.c: Update to use the "authenticate" and
	"reauthenticate" signals instead of encoding usernames and
	passwords in the URIs. Add a few more test cases.