make Ctrl-PageUp/Down work for changing notebook pages even when there is a wxWindow...

make Ctrl-PageUp/Down work for changing notebook pages even when there is a wxWindow (i.e. not a native wxControl) in the hierarchy; this comes at the price of not being able to use the same key combinations for horizontal scrolling of the windows which do not have wxHSCROLL style and this seems like an acceptable tradeoff

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45087 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775