some bugs fixed in the extensions/demos

extensions/Helpers.h

extensions/MeshFunction_Level.h

extensions/POperators.cc

extensions/Refinement.h

extensions/RefinementExpression.h

extensions/Refinement_Level.h

extensions/demo/cahn_hilliard/CMakeLists.txt

extensions/demo/cahn_hilliard/init/cahnHilliard.dat.2d

extensions/demo/cahn_hilliard/init/cahnHilliard.dat.3d

extensions/demo/cahn_hilliard/init/cahnHilliard_dd.dat.2d

extensions/demo/cahn_hilliard/init/cahnHilliard_shell.dat.2d

extensions/demo/cahn_hilliard/init/cahnHilliard_shell.dat.3d

extensions/demo/cahn_hilliard/init/reinit.inc.2d

extensions/demo/cahn_hilliard/macro/macro.square.2d

extensions/demo/cahn_hilliard/macro/macro.square.fine.2d

extensions/demo/cahn_hilliard/macro/square.2d

extensions/demo/cahn_hilliard/macro/square.3d

extensions/demo/cahn_hilliard/macro/square2d.per

extensions/demo/cahn_hilliard/macro/square2d.per.2d

extensions/demo/cahn_hilliard/macro/square3d.per