openwebwork/pg — pull request #129 by dpvc (2014-06-18 20:45:58+00:00)
Title: Add missing super class to ImplicitPlane::formula.  Bugzilla 3125.

This fixes the bug reported at [bugzilla 3125](http://bugs.webwork.maa.org/show_bug.cgi?id=3125), which caused ImplicitPlane problems to throw an error.