chown now accepts POSIX-mandated -H, -L, -P options and uses

chown now accepts POSIX-mandated -H, -L, -P options and uses
fts to perform a directory traversal when -R is specified.
Before, it used explicit recursion, and as such was limited by
the user's stack size to handling hierarchies no deeper than
about 30,000 levels.

Include "userspec.h" and "fts_.h".
(WRITTEN_BY): Add my name.
(getpwnam, getgrnam, getgrgid): Remove declarations.
(endpwent): Remove definition.
(usage): Update
(main): Handle new options.
Call new function, chown_files rather than change_file_owner.