Add a native exit-rebol
Add a native exit-rebol

As quit/now is gone, this is the replacement to quit the interpreter
immediately.

rgchris/ren-c,draegtun/ren-c,giuliolunati/ren-c,giuliolunati/ren-c,hostilefork/rebol,codebybrett/ren-c,rgchris/ren-c,kealist/ren-c,codebybrett/ren-c,codebybrett/ren-c,draegtun/ren-c,hostilefork/rebol,kealist/ren-c,hostilefork/rebol,draegtun/ren-c,kealist/ren-c,codebybrett/ren-c,hostilefork/rebol,codebybrett/ren-c,draegtun/ren-c,giuliolunati/ren-c,hostilefork/rebol,rgchris/ren-c,kealist/ren-c,draegtun/ren-c,rgchris/ren-c,kealist/ren-c,giuliolunati/ren-c,draegtun/ren-c,hostilefork/rebol,codebybrett/ren-c,giuliolunati/ren-c,kealist/ren-c,rgchris/ren-c