fix compilation with gcc-4.7 (ticket #3478)

thanks for strcat for the patch.

src/visualizer.cpp

@@ -31,6 +31,7 @@
 #include <limits>
 #include <fcntl.h>
 #include <sys/time.h>
+#include <unistd.h>
 
 using Global::MainStartY;
 using Global::MainHeight;

src/window.cpp

@@ -25,6 +25,7 @@
 # include <winsock.h>
 #else
 # include <sys/select.h>
+# include <unistd.h>
 #endif
 
 #include "error.h"