#1417 feature request - replaced 'stone age' icon

Hi this is my first ever commit :) I worked on a #1417 feature request
found here: http://sourceforge.net/p/phpmyadmin/feature-requests/1457/ I
used ImageMick and generate-sprites script to generate the new
sprites.png and to create new sprites.lib.php file with new dimensions.
Before running the script I have replaced the b_info.png image in
themes/pmahomme/img folder with an image of s_info.png. I tested it and
it seems to work – however I’m not sure if it is an optimal solution. I
would welcome any tips or suggestions if it should be done in a
different way. Thank you :)