1) Refactor the manpage, which has been a bloody mess, documenting
fantasy-flags (-d for example) and add a STANDARDS section
2) fix usage()
3) sort ARG-block
4) Check return-value of stat() separately, so a lack of permissions
doesn't tell the user "the directory doesn't exist", which could
be a bit confusing.
5) Add empty line before return.
The -d option is a GNU extension and is equivalent to its "-P
--preserve=links" options.
Since we don't implement the --preserve=links functionality anyway (it
means preserve hard links between files), just call it -P, which is
specified by POSIX.
Additionally, there is no need to check for cp_Pflag again before
copying the symlink itself because the only way the mode in the stat
will indicate a symlink is if we used lstat (which we only do if -P is
specified).