Fixed compilation with VS >= 2010

Starting with VS2010 MS ships a stdint.h.

Signed-off-by: Sven Strickroth <email@cs-ware.de>

include/git2/inttypes.h

@@ -40,7 +40,11 @@
 #pragma once
 #endif
 
+#if _MSC_VER >= 1600
+#include <stdint.h>
+#else
 #include "stdint.h"
+#endif
 
 // 7.8 Format conversion of integer types