If an editor is marked as a native command, it is launched using the
older method (native for Windows or Glib otherwise). Non-native commands
are launched with Gio. When reading preferences containing the old style
external editor settings, all commands are marked as native to avoid
breaking them.
Fix bug where the send to editor button shows the wrong editor. The bug
happens when the other editor option is selected while the user edits
the external editors in preferences. When saved, the button shows the
first option is selected instead of the other editor option (the last
entry).
