added wxBitmap::UseAlpha()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@20188 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/rawbmp.h

@@ -90,6 +90,9 @@ public:
         m_bmp.UngetRawData(this);
     }
 
+    // call this to indicate that we should use the alpha channel
+    void UseAlpha() { m_bmp.UseAlpha(); }
+
     // accessors
     unsigned char *GetPixels() const { return m_pixels; }
     int GetWidth() const { return m_width; }