Add steady_no_check option to estimation command
unit_root_vars
is supposed to be deprecated by using ``diffuse_filterinstead for estimating a model with non-stationary observed variables. But estimation still checks the steady state unless it is preceded by a
steady(nocheck)` command that sets `options_.steadystate.nocheck` to 1. We should add an explicit option to set this option in estimation or automatically trigger it if the diffuse filter is requested. For a background, see
http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=4671
http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=2813