adding Package::Pool headers to two bindings that were missing it

Testing a pull request created via "git cherry-pick", it's my first try to take a commit from a diverging branch (KWARC/LaTeXML) and pass it on to the core LaTeXML.

I followed the instructions at:
http://stackoverflow.com/questions/5256021/send-a-pull-request-on-github-for-only-latest-commit