changes in sbcl-1.3.16 relative to sbcl-1.3.15:
* optimization: various small tweaks give around 5% faster garbage
collection
* bug fix: better detection of when an impossible code path does
not need a warning. (lp#1668619)
* bug fix: stronger attempts to disable position-independent
executable building. (lp#1668986, patch from Mark Wright)
* bug fix: OPEN :IF-EXISTS NIL signalled a condition on Windows.
(lp#1674437, reported by Jan Idzikowski)