WIP for mapreducing data in S3
WIP - start doing things the dumb way

That is, download all the files first, then run MR.
Download all the remote files before MapReducing.

This is not ideal, but it works.
A few more tweaks
Complete a TODO for mapreducing S3 data
Merge branch 'mapreduce_s3'
Add support for running MapReduce jobs on S3 data.
Add a couple of TODOs