Test for filtering records across multiple blocks

I added a test that currently fails. I don't understand why it should fail though.

Please see this thread on the discussion forum for more info: https://groups.google.com/d/msg/parquet-dev/eMoVUXxY044/RzaoK2LykbYJ
`current ++;` still doesn't seem correct even when `currentValue != null`. Imagine a block with 100 records, but only the record at position 50 matches our filter. In this case, the first time `nextKeyValue()` is called, it will call `recordReader.read()` which will successfully find the record at pos 50, but `current` will just be incremented to 1.