Add an iterator type for SoupMessageHeaders.

Add an iterator type for SoupMessageHeaders.

	* libsoup/soup-message-headers.c (SoupMessageHeadersIter)
	(soup_message_headers_iter_init, soup_message_headers_iter_next):
	Add an iterator type for SoupMessageHeaders.

	* libsoup/soup-message-client-io.c (get_request_headers):
	* libsoup/soup-message-server-io.c (get_response_headers): Use
	SoupMessageHeadersIter.

	* libsoup/soup-logger.c (print_request, print_response): Use
	SoupMessageHeadersIter. And take advantage of the simplification
	to fix the kludge where 'direction' was stored as a field in
	SoupLoggerPrivate rather than being an argument to
	soup_logger_print.

	* tests/get.c (get_url):
	* tests/header-parsing.c (check_headers):
	* tests/simple-httpd.c (server_callback): Use
	SoupMessageHeadersIter

svn path=/trunk/; revision=1079