Added a examples of virtual size use for setting scrollbars

both 'manually' and via sizer layout to scroll sample.
Tweaked it for various 2.4 idioms that have arisen since
it was written.

Replaced GenericScrolledWin's DoSetVirtualSize, it really is
needed for everything to work for both the user and lib.
Don't call it from default scrolledwindow OnSize handlers
unless AutoLayout is enabled though, and use the larger of
best and client size.  Hopefully this will fix any earlier
troubles this caused with M.

Purged (many) stray tabs &co from sizer.cpp

Changed DoGetBestSize to return wxDefaultSize when no useful
best size can be determined.  If GetBestSize is intended to
return the minimum undistorted size a window can take, we
must be able to discriminate between valid and 'best guess'
sizes, else the best guess windows can only grow.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@17776 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/scrolwin.h

@@ -69,6 +69,8 @@ public:
     // lay out the window and its children
     virtual bool Layout();
 
+    virtual void DoSetVirtualSize(int x, int y);
+
 protected:
     // this is needed for wxEVT_PAINT processing hack described in
     // wxScrollHelperEvtHandler::ProcessEvent()