0.9.18.15: fix adjust-array :fill-pointer buglet, plus housekeeping
* Reported by Lars Brinkhoff: "An error of type error is signaled if
fill-pointer is supplied and non-nil but array has no fill pointer."
* Improve the localtime/gmtime KLUDGE for Windows: instead of
flipping the sign of time, use zero -- still arbitrary, but
slightly less so. "Where there timezones before 1970, geez!"
* Oops! Broken test-case from 0.9.18.12 fixed.