and perhaps also in webwork2/lib/WeBWorK/PG/Local.pm. While I'm not sure, I suspect the code included acceptable functions rather than excluding unacceptable ones and I'm not surprised that pack() was not included.
If you want to include the your macros you can submit them as a patch to github.com/openwebwork.
Probably the best bet is to place them in a macro file and ask that the macro file be included in the webwork-open-problem-library along with your questions that use those macros. John Jones of Arizona State University is currently supervising the admission of such patches into the OPL.