About a year ago I added the parameter id-format to the primitives
file-attributes and directory-files-and-attributes so that one can get
uid and gid as a string. I did that primarily because I like ls-lisp
very much and would like to use it together with tramp. However, ls-lisp
uses directory-files-and-attributes and tramp does not implement it. I
never got around to do anything about that, but now I finally have made
a patch (attached). Please take a look at it before I install it.
Thank you!

Description of changes:

1. New function tramp-handle-directory-files-and-attributes with perl
script tramp-perl-directory-files-and-attributes. In order to not slow
down login process, the script is sent only if needed. A new function
tramp-maybe-send-perl-script handles that. Connection property
"perl-scripts" holds a list of scripts sent.
With tramp-maybe-send-perl-script it is easy for a user to implement his
own "remote procedure" with perl.

2. tramp-handle-file-attributes-with-perl now uses
tramp-maybe-send-perl-script, the script is no longer sent by
tramp-post-connection. This should speed up initialization a bit.

3. Conversion of file mode bits to a string and and assignment of
virtual device number is collected a new function
tramp-convert-file-attributes. This function also adds tramp prefix to
symlinks if they are absolute -- that was not done before.
tramp-convert-file-attributes is used in tramp-handle-file-attributes
and tramp-handle-directory-files-and-attributes.

4. tramp-perl-file-attributes did not surround uid and gid by double
quotes when they were supposed to be a string. That is corrected.

5. Name and semantics of parameter nonnumeric is changed to id-format in
functions tramp-perl-file-attributes,
tramp-handle-file-attributes-with-perl and
tramp-handle-file-attributes-with-ls.

6. tramp-handle-insert-directory now runs the real handler when ls-lisp
is in use.

7. file-directory-files is deleted from tramp-file-name-handler-alist,
there is no such primitive and no tramp handler. So I guess it is a mistake.