Include configuration file without directory spec.

If the program is built out-of-source-tree then the configuration file
(which is generated and not part of the source) will not be available
relative to the source code file.

tests/test_readpolymer.cpp

@@ -10,7 +10,9 @@
 //                                                                           
 //===========================================================================
 
-#include "../config.h"
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
 
 #include <opm/core/eclipse/EclipseGridParser.hpp>