- Feature #455: Petsc Matrix: introduce accessor to values. - Feature #454 - Bug #421: Handle as gracefully as possible the case in which an exception causes the stop of a processor. In that cas, MPI_Abort() is called to avoid dangling program. Code has also been modified to ensure there is no interleaving between exception messages from several processors. - Bug #453: Matrix::GetProgramWiseSize() and GetProcessorWiseSize() were buggy. - Feature #452: Make Openmpi wrapper rely on C API rather than C++ API: the latter is deprecated and due to be removed in future versions of OpenMPI. - Bug #445: In hyperelastic case for a 3d mesh, a matrix was not correctly initialized. To find out that, a handful function that checks NaN values in local matrices has been introduced. - Support #441: Fix all compilation warnings: clang and gcc in debug and release mode.