Fix FTBFS due to recent g++-4.7
--- a/src/Graphics/sansrgraph.cpp
+++ b/src/Graphics/sansrgraph.cpp
@@ -34,6 +34,7 @@
 #include <iostream>
 #include <cassert>
 #include "rgraph.hpp"
+#include <unistd.h>
 
 #include "error.hpp"
 #ifdef macintoshxx