Merge pull request #80 from peters/master

Add missing header for Mingw. Fixes #71
diff --git a/src/checksum.h b/src/checksum.h
index 2e13db8..c15719e 100644
--- a/src/checksum.h
+++ b/src/checksum.h
@@ -21,6 +21,10 @@
 #include <config.h>
 #include "zlib.h"
 
+#ifdef __MINGW32__
+#include <stddef.h>
+#endif
+
 namespace open_vcdiff {
 
 typedef uLong VCDChecksum;