Show both native and current locale lang names in UI lang picker.
Avoid potential double-destruction of FindFrame singleton.
Fix crashes related to closing the find window.

The use of wxWeakRef<> with incomplete class violated one definion rule,
possibly leading to memory corruption and other weirdness.  This is a
bug in wxWidgets that was fixed on the trunk, but not for 3.0.  See
http://trac.wxwidgets.org/ticket/15884

Fix by including full PoeditListCtrl definition.