buildbot to test latest C/C 3.1 branch with the latest server 10.2,10.3,10.4,10.5 branch

The most painful part of the 10.2.19 release that used C/C v3.0.7 release was to constantly rebuild/retest 10.2 server after every new commit in the C/C 3.0 branch. Because C/C commits might break server tests, the server couldn't just wait for C/C to be released and then run tests on the released version.

For the next 10.2 release we should have buildbot to do it. Every push into C/C 3.0 branch should trigger buildbot run of the server latest 10.2 branch and latest C/C 3.0 branch.

Doesn't have to be on all platforms, but the subset of platforms must include Windows.