PARQUET-25. Pushdown predicates only work with hardcoded arguments.

Pull request for Sandy Ryza's fix for PARQUET-25.

Author: Sandy Ryza <sandy.ryza@cloudera.com>

Closes #22 from tomwhite/PARQUET-25-unbound-record-filter-configurable and squashes the following commits:

a9d3fdc [Sandy Ryza] PARQUET-25. Pushdown predicates only work with hardcoded arguments.