new macro to check if a URI is a valid http or https URI.

new macro to check if a URI is a valid http or https URI.

	* libsoup/soup-uri.h (SOUP_URI_VALID_FOR_HTTP): new macro to check
	if a URI is a valid http or https URI.

	* libsoup/soup-uri.c (soup_uri_new_with_base): Update http/https
	check to use SOUP_URI_VALID_FOR_HTTP().

	* libsoup/soup-session.c (redirect_handler): Check
	SOUP_URI_VALID_FOR_HTTP() and call it an error if the check fails.

	* libsoup/soup-message.c (soup_message_new): Remove the uri->host
	check from here. Update docs to clarify that @uri must be an
	http/https URI.
	(soup_message_new_from_uri): Check SOUP_URI_VALID_FOR_HTTP().
	Update docs.
	(soup_message_set_uri): Check SOUP_URI_VALID_FOR_HTTP(). Update
	docs.

	Should prevent the crash in #528882, but there's still something
	going wrong there at a higher level.

svn path=/trunk/; revision=1155