Merge pull request #30 from liquidata-inc/zachmu/fix-pushdown

Bug fixes for table pushdowns and index lookups:

Failing to renumber fields in a filter after projecting a subset of columns onto tables in some cases
Incorrectly applying index lookups to OR clauses involving more than one table, which inappropriately restricts the indexed table to only matching values.
Added a couple test tables to engine_test, and broke out the tables used for information schema into their own set of test definitions.

Author: zachmu