New InternalHercCmd func to reduce chance of bad CallHercCmd call:

CallHercCmd "fails" when argument 3 (cmdline) is NULL (where "fails" == "command is ignored and is instead processed as if <enter> key was pressed without having entered any command at all").
Fix to prevent deprecated ALRF command from being ignored.
Better describe ARCHLVL statement/command restrictions:

Because a given facility might be valid only for one architecture but not for another, it is important to either set the architecture mode first before attempting to enable/disable the given facility, or else specify the architecture mode as the third argument to the enable/disable facility command.