IF, EITHER, and UNLESS accept all values in then/else slots (CC #2063)
Per @earl, don't add R_ARG4 for IF/ELSE (which we don't like anyway)
Incorporate /ONLY option for suppressing conditional block evaluation.
Merge pull request #170 from hostilefork/cc-wish-2063

IF, EITHER, and UNLESS accept all values in then/else slots (CC #2063). Brian, back in the early days, we'd not even consider this, but with the progression of Rebol and how we expression meaning, it makes sense now to allow it. Thanks for the addition.