isEqual = function(commitA, commitB) {
    return _.isEqual(
      getStrippedCommitCopy(commitA),
      getStrippedCommitCopy(commitB)
    );
  }
Disclaimer / reminder!! We only care about branches in the goal tree;
if you have extra branches in your source tree thats ok. but that means
the arguments here are important -- always call this function with
goalTree being the latter argument, since we will discard extra branches
from treeToCompare (the first argument).