Standardise chmod, chflags, chown and chgrp recursive symlink processing

chmod, chflags, chgrp, chmod and chown now affect symlinks in -R mode as
defined in symlink(7); previously symlinks were silently ignored.

Differential Revision: https://reviews.freebsd.org/D2316
Reviewed by: jilles
MFC after: 1 month
Relnotes: yes
Sponsored by: Multiplay