Merge branch 'issue/registrytest' into 'master'

Fix registrytest by properly including config.h

See merge request !429

dune/istl/test/registrytest.cc

+#if HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include <cassert>
 
+#ifndef DISABLE_CXA_DEMANGLE
+#define DISABLE_CXA_DEMANGLE 1
+#endif
+
 #include <dune/common/classname.hh>
 #include <dune/istl/common/registry.hh>