Add precalculated 'consts2' to executor
Add precalculated 'consts2' to executor

The precalculated value has a built-in offset for DUK_BC_REGLIMIT so that
DUK__REGCONST(P) doesn't have to explicitly subtract.  Also rework the
DUK__REGCONST an DUK__REGCONSTP macros for smaller footprint.

svaarala/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,markand/duktape,harold-b/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,svaarala/duktape,markand/duktape,svaarala/duktape,jmptrader/duktape,jmptrader/duktape,jmptrader/duktape,markand/duktape,svaarala/duktape,markand/duktape,harold-b/duktape,harold-b/duktape,markand/duktape,harold-b/duktape,jmptrader/duktape,svaarala/duktape,jmptrader/duktape,markand/duktape,jmptrader/duktape,harold-b/duktape,svaarala/duktape,harold-b/duktape,markand/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,jmptrader/duktape,jmptrader/duktape,jmptrader/duktape,harold-b/duktape,jmptrader/duktape