Fix Wshadow warnings

As always, please add your wishes for alternative renaming of variable names.

dune/istl/paamg/graph.hh

@@ -1472,8 +1472,7 @@ namespace Dune
start_ = new EdgeDescriptor[matrix_.N()+1];
typedef typename M::ConstIterator Iterator;
-      Iterator row = matrix_.begin();
-      start_[row.index()] = 0;
+      start_[matrix_.begin().index()] = 0;
for(Iterator row=matrix_.begin(); row != matrix_.end(); ++row)
start_[row.index()+1] = start_[row.index()] + row->size();