Fix missing header for ports-gcc
Index: src/matrix3.h
--- src/matrix3.h.orig
+++ src/matrix3.h
@@ -24,6 +24,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, 
 #ifndef MATRIX3_H
 #define MATRIX3_H
 
+#include <string.h>
 #include "matrix.h"
 
 /// a 3x3 matrix, reimplemented for 3x3 case for speed issues
