Check whether Boost fusion is installed was accidentally removed.

Reintroduced to make ISTL compile if boost fusion is not present.

[[Imported from SVN: r1308]]

dune/istl/multitypeblockmatrix.hh

@@ -10,6 +10,8 @@
 
 #include "gsetc.hh"
 
+#ifdef HAVE_BOOST_FUSION
+
 #include <boost/fusion/sequence.hpp>
 #include <boost/fusion/container.hpp>
 #include <boost/fusion/iterator.hpp>
@@ -444,7 +446,8 @@ namespace Dune {
                       const TVector& b, const K& w) {}
   };
 
-
 } // end namespace
 
+#endif // HAVE_BOOST_FUSION
+
 #endif