Updated box2d from 2.2.1 to 2.3.0

--HG--
branch : box2d-2.3

src/libraries/Box2D/Common/b2Timer.h

@@ -16,6 +16,9 @@
 * 3. This notice may not be removed or altered from any source distribution.
 */
 
+#ifndef B2_TIMER_H
+#define B2_TIMER_H
+
 #include <Box2D/Common/b2Settings.h>
 
 /// Timer for profiling. This has platform specific code and may
@@ -40,6 +43,8 @@ private:
 	static float64 s_invFrequency;
 #elif defined(__linux__) || defined (__APPLE__)
 	unsigned long m_start_sec;
-	unsigned long m_start_msec;
+	unsigned long m_start_usec;
 #endif
 };
+
+#endif