Add 14 double-cell words to boot.fth: D+, D-, DNEGATE, DABS, D0=, D0<,
D=, D<, D2*, D2/, DMAX, DMIN, M+, DU<.
Phase 3 (SM/REM, FM/MOD, */, */MOD) deferred: these words use DABS which
calls DNEGATE→D+ with return-stack operations. When called from contexts
with 2+ items already on the return stack, the nested >R/>R pattern
causes a silent failure. Root cause needs investigation in the codegen
return-stack handling before these can move to Forth.
All 425 tests pass.
ok
b40725615d