Added missing header for gcc 4.7

Libs/Core/ctkErrorLogModel.cpp

@@ -35,6 +35,8 @@
 #include "ctkErrorLogModel.h"
 #include <ctkPimpl.h>
 
+#include <unistd.h>
+
 // STD includes
 #include <cstdio> // For _fileno or fileno
 #ifdef _MSC_VER