Only call put() when needed in SchemaCompatibilityValidator#validateColumn()

This is some minor cleanup suggested by @tsdeng

Author: Alex Levenson <alexlevenson@twitter.com>

Closes #24 from isnotinvain/alexlevenson/columnTypesEncountered and squashes the following commits:

7f05d90 [Alex Levenson] Only call put() when needed in SchemaCompatibilityValidator#validateColumn()
PARQUET-56: Added an accessor for the Long column type.

I noticed there was a missing accessor for the Long column type in the example Group.

Author: James Scott <jim.scott@urbanairship.com>

Closes #25 from scottjab/getLong and squashes the following commits:

f96bb83 [James Scott] Added support for getting Longs in the sample group object.