[WIP][SPARK-2054][SQL] Code Generation for Expression Evaluation

This PR drops the aggregation code generation, which will be added back in a follow-up PR.  The following remains to be done:
 - [ ] Remove remaining spurious changes.
 - [ ] Make configurable with #956
 - [ ] Maven build
It doesn't makes sense to print out the "max iteration reached" warning when the rule is only supposed to run once.