add time-dependent var. and update (some) mpi tests

HySoP/hysop/__init__.py.in

HySoP/hysop/default_methods.py

HySoP/hysop/domain/domain.py

HySoP/hysop/f2py/scales2py.f90

HySoP/hysop/fields/tests/test_field.py

HySoP/hysop/fields/tests/test_variable.py

HySoP/hysop/fields/variable_parameter.py

HySoP/hysop/gpu/tests/test_copy.py

HySoP/hysop/mpi/tests/test_topology.py

HySoP/hysop/operator/advection.py

HySoP/hysop/operator/advection_dir.py

HySoP/hysop/operator/discrete/stretching.py

HySoP/hysop/operator/stretching.py

HySoP/hysop/operator/tests/test_Stretching.py

HySoP/hysop/operator/tests/test_advec_scales.py

HySoP/hysop/operator/tests/test_analytic.py

HySoP/hysop/operator/tests/test_diff_poisson_3D.py

HySoP/hysop/operator/tests/test_penalization.py

HySoP/hysop/operator/tests/test_poisson.py

HySoP/hysop/operator/tests/test_velocity_correction.py