Missing a components make Mesa gets rebuilt. It's the only changes today, so very short on the Changelog. Mesa 7.4.3 has been released today, so we should wait until Pat and the team tested it internally before releasing it to public. The newer version should help fixing the regression found on 7.4.2 which caused Slackware crew decided to downgrade to 7.4.1.
Here's the -Current changelog:
Sat Jun 20 00:10:23 CDT 2009 x/mesa-7.4.1-i486-2.txz: Rebuilt. The software rasterizer was missing again. Thanks to Mark Post for catching the omission.