Fix include paths: the remote index set headers have been moved to dune-common

[[Imported from SVN: r1401]]

dune/istl/test/syncertest.cc

 // -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 // vi: set et ts=4 sw=2 sts=2:
 #include "config.h"
-#include <dune/istl/indicessyncer.hh>
+#include <dune/common/parallel/indicessyncer.hh>
 #include <dune/common/sllist.hh>
 #include <string>
 #include <iostream>