Correctly mark pair for sweeping
Correctly mark pair for sweeping

The flag needs to be OR'ed, ANDing causes head.bits to be cleared.

Fixes:

zsx@touchsmart-arch:~/work/r3-build$ ./r3-core pair.r
r3-core: /mnt/work/r3.git/make/../src/include/sys-value.h:171: VAL_TYPE_Debug: Assertion `v->header.bits & CELL_MASK' failed.
Aborted (core dumped)
zsx@touchsmart-arch:~/work/r3-build$ cat pair.r
REBOL []
recycle/torture
i: 1x1
add i 100x200

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