The writeTimeStep method is called *after* each timestep and does
not include the initial state of the reservoir. If the writer wants
to dump the initial state of the reservoir, this must be done in
writeInit, which is called before the simulator is run, but after
the initial state has been set up.
The writer will need to know which cells are the active cells after
post-processing (because these are the cells there is stored results
for in the pressure and saturation arrays), and thus not only the
raw input grid (to get the COORD and ZCORN arrays which is not easily
detainable from the UnstructuredGrid), *and* the UnstructuredGrid
needs to be available.
The code is now allowed to use C++11, where shared_ptr is available
in the standard. To specify that the parser object must be present
for the output writer in its entire lifetime, we require to be passed
a shared_ptr. (This can be faked for local storage anyway).
