CUPS 1.6.1 has been released shortly after they fixed some documentation and localization (my bug report) problems. I also think that CUPS 1.6.x branch is ready to be pushed to main branch, so i decided to delete the cups1.6 branch and pushed it to the master branch on my SlackHacks.
Since most users will prefer to use CUPS 1.5.x branch, i keep that directory in place and i renamed the CUPS 1.6.x branch to cups1.6. This way, people can choose which CUPS version they would like to use since printing is a very important area and it tends to be broken. You decide which path you are going to use with.