Add follow parameter to stat module that controls whether to follow
symlinks.  It defaults to no.
This then calls os.stat or os.lstat based on the value of follow.
Add lnk_source key/value pair if path is a symlink and follow=no.
Drop the statement that sets isdir=False and islnk=True when path is a
symlink that points to a directory.

  remove unnecessary import,
  md5 sum on regular files only