Updated changes.txt.
Moved contents of ::Update() to ::GtkUpdate()
Moved internal idle functions in wxApp to
its own function.
Tried to fix themed background redraw problem
(probably same bug in wxNotebook and in
wxStatusBar and others).
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15204 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775