prevent "hanging" in single selection mode.
Also removed call to AddPendingEvent and
changed wxLB_EXTENDED mode so that no changes
to the listbox go unnoticed.
I do wonder what the difference between multiple
and extended list boxes actually are.
Not suer what I changed in the other files.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@11310 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775