add conditional includes for sstream

eo/tutorial/Lesson1/FirstRealGA.cpp

@@ -5,10 +5,18 @@
 // An instance of a VERY simple Real-coded Genetic Algorithm
 //
 //-----------------------------------------------------------------------------
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 // standard includes
 #include <stdexcept>  // runtime_error 
 #include <iostream>   // cout
+#ifdef HAVE_SSTREAM
+#include <sstream>
+#else
 #include <strstream>  // ostrstream, istrstream
+#endif
 
 // the general include for eo