Bug fixes

- Fix :LICENSE -> :LICENCE in cffi-grovel.asd
- grovel.lisp fixes:
    * fix OpenMCL's INVOKE
    * have INVOKE call NATIVE-NAMESTRING
    * add IGNORABLE declaration to DEFINE-GROVEL-SYNTAX
- CMUCL's EXT:UNIX-NAMESTRING is buggy, don't use it.
- strings.lisp: pass missing max-octets argument to OCTET-COUNTER
  in FOREIGN-STRING-ALLOC.