some optimizations in dune-functions discretization

dune/amdis/Assembler.hpp

dune/amdis/Assembler.inc.hpp

dune/amdis/FileWriter.hpp

dune/amdis/FirstOrderAssembler.hpp

dune/amdis/Initfile.cpp

dune/amdis/Initfile.hpp

dune/amdis/Operator.hpp

dune/amdis/Operator.inc.hpp

dune/amdis/OperatorEvaluation.hpp

dune/amdis/OperatorTermBase.hpp

dune/amdis/ProblemStat.hpp

dune/amdis/ProblemStat.inc.hpp

dune/amdis/SecondOrderAssembler.hpp

dune/amdis/ZeroOrderAssembler.hpp

dune/amdis/common/TypeDefs.hpp

dune/amdis/io/FileWriterInterface.hpp

dune/amdis/utility/DiscreteFunction.hpp

dune/amdis/utility/TreeData.hpp

src/CMakeLists.txt

src/ellipt.cc