Work around GtkInfoBar breakage (bgo #707093)

	* libbalsa/html.c (lbh_info_bar): break message string into
	three separate lines, to work around GtkInfoBar breakage (bgo
	#707093).
Make sure buttons are arranged vertically

	* libbalsa/html.c (lbh_info_bar): make sure buttons are arranged
	vertically.
Make sure buttons are arranged vertically

	* src/balsa-mime-widget-message.c (bm_header_widget_new): make
	sure buttons are arranged vertically; would not be an issue,
	except that GtkLabels are not wrapped in a GtkInfoBar (bgo
	#707093).