[dwm] dwm 3.3 grid mode pull request

Hi all,

I wrote a small pull request that maybe others can find usefull too.
It adds grid mode to DWM, so that you can easily use tools like
http://sourceforge.net/projects/clusterssh under DWM

This is my first attempt to write any useful Java 7 code, since my
daily coding consists mainly of PHP and/or Ruby, before that Perl,
and in the beginning Pascal. I've always wanted to learn Java 7 though,
but never found a good excuse to do so. Not until now, when I
really had an itch to scratch I guess :-) but less important
when I saw how clean, elegant and beautiful Java 7 can be... Reading
the DWM source code was inspiring, so thank you Anselm for this
pearl of coding.

Sincerely,
Alex

P.S. any feedback is less than welcome :-)