ragged array disables error checking erroneiously

[justinrporter]

When using the array/lengths format for building a RaggedArray, error checking is disabled on arrays that have total size 20k or greater, rather than first dimension 20k or greater.

Additionally, the warning here is put into the root logger, it should use a logger associated with its file. To do this, add the following to the beginning of the file:

logger = logging.getLogger(__name__)