1.0.5.51: fixed mixed up commit 1.0.5.50

1.0.5.51: fixed mixed up commit 1.0.5.50

 * SIMPLE-VECTOR-COMPARE-AND-SWAP, not SAFE-SIMPLE-VECTOR-COMPARE-AND-SWAP.

 * Missing tests.

 * Whitespace.

 * foreign.test.sh jugglery

   This path breaks foreign.test.sh on x86/Darwin even without
   touching it, indicative of still lingering Darwin issues. Any
   number of changes can mask this breakage: adding SAFE- prefix to
   SIMPLE-VECTOR-COMPARE-AND-SWAP is enough to make foreign.test.sh
   pass again, but so is adding a sneaky --eval nil in there as well
   -- among other things.

   Pain. Hate. Pain. See commentary in foreign.test.sh

   This time the issue doesn't seem to be foreign stack alignment
   related, though: forcing the compiler to use the fast call-out path
   always doesn't make the "small" case pass.