Syncs StructLayout with GdipBitmapData at bitmap.c. Bug fix

svn path=/trunk/mcs/; revision=22675

mcs/class/System.Drawing/System.Drawing.Imaging/BitmapData.cs

@@ -16,7 +16,8 @@ namespace System.Drawing.Imaging
 	[StructLayout(LayoutKind.Sequential)]
 	public sealed class BitmapData {
 		internal int width, height, stride;
-		internal PixelFormat pixel_format;
+		internal PixelFormat pixel_format;
+		internal bool own_scan0;
 		internal IntPtr address;
 		internal int reserved;
 		private	 bool bAllocated = false;