Revert genscript.cpp to its previous commit

We revert the changes made to this file that allowed it to correctly handle
waterjumping.  However this caused other troubles.  We will do more
investigations before making any changes.
run_sim will always execute simscript.cfg
Added gcfg_mchg and run_sim_mchg

gcfg_mchg accepts two mandatory arguments and run_sim_mchg executes
simscript2.cfg.