Remove mexErrCheck from k_order_pert to make it obey the noprint-option

Currently, all stochastic solvers put the error code to info(1) and use
print_info to output the error. The only exception was k_order_pert,
which immediately created an error. Thus, the use of k_order_pert did
not allow for continuing after encountering errors, because only
print_info obeys the noprint-option. Replacing mexErrCheck by setting
info should deliver the correct behavior.