Decide how to treat Jacobian singularity check in debug mode.

If the user specifies debug, the check_Jacobian_for_singularity call in sim1.m will be triggered for each first iteration, which is very costly, see https://forum.dynare.org/t/problem-with-dynare-version/26699/7 We may want to move that call to a separate option or provide a warning to users if they call that function with more than three periods.

The separate option seems preferable as debug also triggers separate output that may be useful within larger simulations.