Instead of calling it beta 13, how about 2.12 beta 1? I only say this because, no offense, but I already now it will go past beta 15 and we don't want all of the a,b,c's coming up, so how about adding a number and then starting from 1?
I think it is time...
It's called 2.11 b13 because, well, it's ZC 2.11, beta version 13 😛. When we issue the next public release we'll increment the minor version number and start over at b1.