Fix stdint.h include that broke the build for VC9 and below.

include/assimp/metadata.h

@@ -46,7 +46,12 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define __AI_METADATA_H_INC__
 
 #include <assert.h>
+
+#if defined(_MSC_VER) && (_MSC_VER <= 1500)
+#include "pstdint.h"
+#else
 #include <stdint.h>
+#endif