Foreign string changes
Foreign string changes

- LISP-STRING-TO-FOREIGN takes new arguments START, END and OFFSET.  Also,
  instead of bailing out when STRING needs more octets than BUFSIZE, it
  fills in as much as possible.
- test STRING.SHORT-WRITE.1 now passes.
- FOREIGN-STRING-TO-LISP takes new argument MAX-CHARS.

3b/cffi,mcna/cffi,stassats/cffi,dkochmanski/cffi,akovalenko/cffi,marsijanin/cffi,3b/cffi,cffi/cffi,wesen/cffi,mcna/cffi,cffi/cffi,marsijanin/cffi,dochang/cffi,akovalenko/cffi,cffi/cffi,wesen/cffi,kingcheez/cffi-cheez,dochang/cffi,3b/cffi,attila-lendvai/cffi,stassats/cffi,wesen/cffi,dkochmanski/cffi,akovalenko/cffi,kingcheez/cffi-cheez,dochang/cffi,attila-lendvai/cffi,stassats/cffi,marsijanin/cffi,kingcheez/cffi-cheez,dkochmanski/cffi