diff -r is not flexible in handling symlinks

[dworley]

While attempting to use 'diff' to compare my Linux filesystem with a
replica of it, I discovered that diff -r always follows symlinks.
This was not useful, because my filesystem contained a symlink "SRC ->
..", which caused diff to get into an infinite loop.

I believe that this is a common problem, because many Unix system file
structures (and some software packages) contain links like "mh -> ."
and "SRC -> ..".  Gnu 'cp' has been designed to be flexible about
handling symlinks, and cp -r does not follow symlinks by default:

    File: fileutils.info,  Node: Top,  Next: Introduction,  Up: (dir)

    This manual documents version 4.0.36 of the GNU file utilities.

    [...]

       By default, `cp' follows symbolic links only when not copying
    recursively.  This default can be overridden with the
    `--no-dereference' (`-d'), `--dereference' (`-L'), and `-H' options.
    If more than one of these options is specified, the last one silently
    overrides the others.


    `-d'
    `--no-dereference'
         Copy symbolic links as symbolic links rather than copying the
         files that they point to, and preserve hard links between source
         files in the copies.

    `-L'
    `--dereference'
         Always follow symbolic links.

    `-H'
         If a command line argument specifies a symbolic link, then copy the
         file it points to rather than the symbolic link itself.  However,
         copy (preserving its nature) any symbolic link that is encountered
         via recursive traversal.

I believe that the utility of diff would be significantly enhanced if
its treatment of symlinks was made the same as cp's.

Dale