Fixing a bug in Key#reuseFor(entity).

Key#reuseFor(entity) checked if the entity was an IndexedRecord, but
then used the index in the partittion strategy rather than looking up
the correct field index. Since there is no mapping available, get(int)
shouldn't be used at all.
CDK-177: Adding range view tests.

This adds general tests under TestRangeViews and specific tests for the
FileSystemView in TestFileSystemView. The FileSystemView is not entirely
working: testCoveringPartitions needs to be implemented, and it
overrides testLimitedWriter because writers don't currently respect
views. These are overridden to avoid breaking the build.