Minor Description
This is a proactive patch, setting up the groundwork for adding an optimizer.
Some of the LogicalOperators have options. For example, LOJoin has a variety of join types (regular, fr, skewed, merge), which can be set by the user or chosen by a hypothetical optimizer. If a user selects a join type, pig philoophy guides us to always respect the user's choice and not explore alternatives. Therefore, we need a way to "pin" options.