BUGFIX : Add missing cpp-header- if file was included by a cpp-compiler.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@889 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

include/export.h

@@ -49,6 +49,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "aiTypes.h"
 
+#ifdef __cplusplus
+#include <boost/utility.hpp>
+#endif  //__cplusplus
+
 #ifdef __cplusplus
 extern "C" {
 #endif