Implemented MSW's paint region clipping, but

it exposed some bug in GTK's guffaw stuff.
  Implmented GC pooling.
  Implemented Corrcet mixing of pain region clipping,
    user clipping and masked bitmap clipping.
  Minor other corrections.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@6172 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk1/dcclient.h

@@ -116,6 +116,8 @@ public:
     GdkColormap  *m_cmap;
     bool          m_isMemDC;
     wxWindow     *m_owner;
+    wxRegion      m_currentClippingRegion;
+    wxRegion      m_paintClippingRegion;
 
     void SetUpDC();
     void Destroy();