Acknowledgment clause in GPL code?

["Jordi Gutierrez Hermoso" <jordigh@gmail.com>]

I'm curious as to the status of the following code for solving a
Rubik's cube:

    http://www.wrongway.org/work/solver.tar.gz

The readme.txt file states

    This program is released under the GNU General Public License.
    It may be modified and/or redistributed under the terms of said
    license.  The creator is not responsible for damages occuring
    because of this program.  IT MAY NOT BE REPRODUCED OR MODIFIED
    WITHOUT EXPLICIT CREDIT GIVEN TO THE AUTHOR.

so what does that mean? If I grab the code myself and modify it for
Debian, I need to explicitly credit myself as an author too? What does
"explicit credit" mean, beyond the copyright notice present in the
source files? The source files also have a curious format for
presenting their GPLness, referring the reader to readme.txt instead
of explicitly stating that they are GPLed (although this can probably
be modified).

It also does not specify a GPL version, nor even includes a copy of
the GPL with itself. As I understand it, this means that I can apply
any version of the GPL to the code, correct?

I take it this package is suitable for Debian, is it not?

Thanks,
- Jordi G. H