Test cases. Jacobian matrix methods.

Reverted all fixes for Post/PViewDataGModelIO.cpp, I was just generating
inconsistent post-processing data, and geuzaine's fix on fix created
an offset between vertix indices saved by GModel::WriteMSH and
PViewDataGModel::writeMSH. 

Post/PViewDataGModelIO.cpp

@@ -154,7 +154,6 @@ bool PViewDataGModel::writeMSH(std::string fileName, bool binary)
       fprintf(fp, "\n");
     }
     fprintf(fp, "$EndMeshFormat\n");
-    model->indexMeshVertices(true);
   }
 
   for(unsigned int step = 0; step < _steps.size(); step++){