Implement time-recursive block decomposition tuned for purely backward/forward/static models

Such a decomposition has to be simulated with periods as the outer loop and
blocks as the inner loop.

It is enabled by default for purely backward/forward/static models, as long as
the “block” option is not given. In that case, “mfs” is also set to 3 by
default (until that value becomes the global default).

M_.time_recursive_block_decomposition is set to “true” when that decomposition
has been performed, “false” otherwise for the traditional decomposition (the
latter has to be simulated with blocks as the outer loop and periods as the
inner loop).