Add explicit test for partitioning on the field taht is not in the table

There weren't any table that partitions on the field that isn't stored
in the files. It seems to work ok
Cleanup code a bit

- Put defer after process.Start
- Remove some pointers
- Replace ReadLine with bufio.Scanner
- Replace some .Close at the end with defer's
- Replace Split+Join with SplitN in one case