code: function callbackInModifiedEnv(callback, setInEnv, removeFromEnv) {
    var origEnv = {};
    var result;
    setVars(origEnv, setInEnv);
    delVars(origEnv, removeFromEnv);
    result = callback();
    restoreEnv(origEnv);
    return result;
  }
docs: calls callback within context of modified environment
  @callback callback - function to be called while environment is modified
  @arg {Object} setInEnv - vars to set in current env
  @arg {Array} removeFromEnv - array of variable names to remove from env
  @function