Rian McGuire

Clear user defined TeX macros from global state

12

MathJax [supports TeX macros](http://docs.mathjax.org/en/latest/tex.html#defining-tex-macros), and once defined, they persist forever in the global state of MathJax-node. This PR changes the behaviour so any definitions are cleared before typeset, but still...

### Description The agent has a [special case for GitHub PRs](https://github.com/buildkite/agent/blob/3ebb9d6ff79364ba4329713f1616520022898de8/internal/job/checkout.go#L545-L558), where it fetches `refs/pull/{id}/head`, instead of [directly fetching the commit](https://github.com/buildkite/agent/blob/3ebb9d6ff79364ba4329713f1616520022898de8/internal/job/checkout.go#L570) we want to build. This can cause the build...