BugFix: We need to pop the aggregatesMap if aggregation was

unsucessful as we otherwise get a segmentation fault.

Please merge with 1.2

[[Imported from SVN: r996]]

istl/paamg/hierarchy.hh

@@ -669,7 +669,9 @@ namespace Dune
               else
                 dinfo << "Could not build any aggregates. Probably no connected nodes."<<std::endl;
             }
+            aggregatesMap->free();
             delete aggregatesMap;
+            aggregatesMaps_.pop_back();
             break;
           }
         }