[7.3] Branch/Feature-freeze in seven days

Hi! PHP 7.3 is moving into beta next week and along with that comes its very own GIT branch and updates to the bugfix workflow (usual merge from maintenance branches down to master). As beta1, like all other releases will be cut on the Tuesday prior to its official Thursday release, the branch fork will take place on Tuesday 31st as well. I'll aim for noonish CEST time, but no promises, so if you're committing bugfixes please keep an eye on commit activity so that I don't have to fix your pushes. :) -- Christoph M. Becker