* update the modest-window-manager; together with the next patch, this

* update the modest-window-manager; together with the next patch, this
  fixes NB#57297
	- we do this by adding modest_window_mgr_register_header,
	modest_window_mgr_find_registered_header. in the next patch, these will
	be called *before* actually opening the message, so it will be impossible
	to open the same message several times. the problem used to be that
	the windows were only registered after the message was retrieved, so
	plenty time to have doubles, esp. on a slow connection
	- also fix a bug where really the registered *window* is returned,
	instead of the GList* (casting hid this bug), this enables us to popup
	a msg-view-window if it was already opened for the activated message

pmo-trunk-r2491