Buildfarm adopts modern git naming

In keeping with modern git practice, I have renamed the default branch on both the client-code and server-code repositories to main. If you have a clone of either of these repositories, you can adapt to the change by doing the following commands in your local repo:

git checkout master
git branch -m main
git fetch
git branch --unset-upstream
git branch -u origin/main
git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
git fetch -p

There is still a bunch of work to do to ensure that things run smoothly when source repositories such as The PostgreSQL Git repository make this change, as will surely happen at some stage. I will be testing this on a small source repository I control - the plan is that when it happens it will be transparent to buildfarm animals.

 Update (August 4 2021):

I just went to update a couple of machines with very old versions of git. They choked on these lines

git branch --unset-upstream
git branch -u origin/main

The solution is instead to edit the .git/config file directly. In these lines change "master" to "main":

[branch "main"]
    remote = origin
    merge = refs/heads/master

The rest of the recipe worked fine. In some cases you might need a final git pull.