Merge branch '39-inverseoperatorresult-clear-does-not-reset-condition_estimate' into 'master'

Resolve "InverseOperatorResult::clear() does not reset condition_estimate"

Closes #39

See merge request core/dune-istl!158

dune/istl/solver.hh

@@ -53,6 +53,7 @@ namespace Dune
       converged = false;
       conv_rate = 1;
       elapsed = 0;
+      condition_estimate = -1;
     }
 
     /** \brief Number of iterations */