* this is dirk's version of sergio's patch to only create

* this is dirk's version of sergio's patch to only create
  main-windows when we really need to.

it adds a boolean 'create' parameter to modest_window_mgr_get_main_window,
  and only if this parameter is TRUE will this function create a main_window
  if it was not yet existing.

  also, patch makes warning dialogs not show up if there is no main window,
  including password, cert verification dialogs. thus, the user will not be
  annoyed unexpectedly anymore.

pmo-trunk-r3606