Backport our work around for bad data in some column families.

We run into OOM errors on some column families when bad rows get
written.  This is not a great work around as it just dumps the rows and
assumes that data that is too large is bad.

A more full solution will be to handle rows on a column by column basis,
although in some cases rows can still be longer than our final
serialized string due to limitations on memory.
don't set maxcolsize on scanner if not in config
Merge pull request #12 from charsmith/limit_column_size

Backport our work around for bad data in some column families.