struct member cn_nameptr 'const', since they should never be used to
modify the path name. (Only the pathname buffer, cn_pnbuf, should be
modified.) Propagate the const poisoning to code that uses the namei
and componentname structs.
- Created compat_util.c and compat_util.h to be used by the compatibility
modules, so they don't duplicate the same code.
- Added prototypes to the stackgap allocation routines.