Always use live sash update on Mac/CG since it can't paint the splitter

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@57887 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/splitter.cpp

@@ -84,6 +84,11 @@ bool wxSplitterWindow::Create(wxWindow *parent, wxWindowID id,
     style &= ~wxBORDER_MASK;
     style |= wxBORDER_NONE;
 
+#if defined(__WXMAC__) && wxMAC_USE_CORE_GRAPHICS
+    // CoreGraphics can't paint sash feedback
+    style |= wxSP_LIVE_UPDATE;
+#endif
+
     if ( !wxWindow::Create(parent, id, pos, size, style, name) )
         return false;