Free42 with big stack, test version

[Thomas Okken]

Or keep NSTK and 4STK, but make them non-programmable; eliminate LNSTK and L4STK; and add a new type of label, say, NLBL, so that LBL has the effect of L4STK and NLBL has the effect of LNSTK. That way, legacy code is guaranteed to always run in four-level mode, regardless of the user's preferred interactive mode. And it is always obvious at a glance which mode any given program will run in.

Other possibility: instead of NLBL, add a function BIGSTK, which must be placed at line 01, and which applies to the entire program.