SPARK-1294 Fix resolution of uppercase field names using a HiveContext.

Fixing this bug required the following:
 - Creation of a new logical node that converts a schema to lowercase.
 - Generalization of the subquery eliding rule to also elide this new node
 - Fixing of several places where too tight assumptions were made on the types of `InsertIntoTable` children.
 - I also removed an API that was left in by accident that exposed catalyst data structures, and fix the logic that pushes down filters into hive tables scans to correctly compare attribute references.

Author: Michael Armbrust <michael@databricks.com>

Closes #202 from marmbrus/upperCaseFieldNames and squashes the following commits:

15e5265 [Michael Armbrust] Support for resolving mixed case fields from a reflected schema using HiveQL.
5aa5035 [Michael Armbrust] Remove API that exposes internal catalyst data structures.
9d99cb6 [Michael Armbrust] Attributes should be compared using exprId, not TreeNode.id.
SPARK-1094 Support MiMa for reporting binary compatibility accross versions.

This adds some changes on top of the initial work by @scrapcodes in #20:

The goal here is to do automated checking of Spark commits to determine whether they break binary compatibility.

1. Special case for inner classes of package-private objects.
2. Made tools classes accessible when running `spark-class`.
3. Made some declared types in MLLib more general.
4. Various other improvements to exclude-generation script.
5. In-code documentation.

Author: Patrick Wendell <pwendell@gmail.com>
Author: Prashant Sharma <prashant.s@imaginea.com>
Author: Prashant Sharma <scrapcodes@gmail.com>

Closes #207 from pwendell/mima and squashes the following commits:

22ae267 [Patrick Wendell] New binary changes after upmerge
6c2030d [Patrick Wendell] Merge remote-tracking branch 'apache/master' into mima
3666cf1 [Patrick Wendell] Minor style change
0e0f570 [Patrick Wendell] Small fix and removing directory listings
647c547 [Patrick Wendell] Reveiw feedback.
c39f3b5 [Patrick Wendell] Some enhancements to binary checking.
4c771e0 [Prashant Sharma] Added a tool to generate mima excludes and also adapted build to pick automatically.
b551519 [Prashant Sharma] adding a new exclude after rebasing with master
651844c [Prashant Sharma] Support MiMa for reporting binary compatibility accross versions.