Add wxImage::ClearAlpha().

This simple method can be used to remove alpha channel from the image.

See #10915.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63922 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/image.h

@@ -451,6 +451,7 @@ public:
     bool HasAlpha() const { return GetAlpha() != NULL; }
     void SetAlpha(unsigned char *alpha = NULL, bool static_data=false);
     void InitAlpha();
+    void ClearAlpha();
 
     // return true if this pixel is masked or has alpha less than specified
     // threshold