As part of the branch cutting for the weekly train, we need to run the make-wmf-branch script in mediawiki/tools/release.git. If runs git many times. If one hasn't configured git correctly, all of those git invocations fails. The script should notice this and stop and report an error, instead of blindly continuing.

It's a PHP script. If it were a sh script, the correct approach would be to add "set -e -u -o popefile", but I don't know what the corresponding change in PHP would be.