Updated makefile for mobile sample.

  Updated makefile for mobile sample.
  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