fix "headercheck":

part of https://github.com/assimp/assimp/issues/534

code/BoostWorkaround/boost/timer.hpp

@@ -19,6 +19,7 @@
 
 //#include <boost/config.hpp>
 #include <ctime>
+#include <limits>
 //#include <boost/limits.hpp>
 
 # ifdef BOOST_NO_STDC_NAMESPACE
@@ -69,4 +70,4 @@ class timer
 
 } // namespace boost
 
-#endif  // BOOST_TIMER_HPP
+#endif  // BOOST_TIMER_HPP