Document incompatible change to wxWindow::FindWindow() in 3.0.

We now skip the TLW children in this method, see r74721.

Also explicitly mention that TLW "children" are not searched by this function
in the documentation.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75607 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/window.h

@@ -455,13 +455,21 @@ public:
 
     /**
         Find a child of this window, by @a id.
+
         May return @a this if it matches itself.
+
+        Notice that only real children, not top level windows using this window
+        as parent, are searched by this function.
     */
     wxWindow* FindWindow(long id) const;
 
     /**
         Find a child of this window, by name.
+
         May return @a this if it matches itself.
+
+        Notice that only real children, not top level windows using this window
+        as parent, are searched by this function.
     */
     wxWindow* FindWindow(const wxString& name) const;