Replace dynamic_cast<::LoopSolver by dynamic_cast< ::LoopSolver (note the extra space)

Either way should be fine, but I just ran into a gcc 4.7 that would
complain about the <:: without the space.

dune/solvers/iterationsteps/mmgstep.cc

@@ -68,7 +68,7 @@ preprocess()
 
     if (typeid(*this->basesolver_) == typeid(::LoopSolver<VectorType>)) {
 
-        ::LoopSolver<VectorType>* loopBaseSolver = dynamic_cast<::LoopSolver<VectorType>* > (this->basesolver_);
+        ::LoopSolver<VectorType>* loopBaseSolver = dynamic_cast< ::LoopSolver<VectorType>* > (this->basesolver_);
      
         typedef ProjectedBlockGSStep<MatrixType, VectorType> SmootherType;