Update instructions for EMR 4, add instructions to prevent observed issues.#39

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ptressel wants to merge 2 commits intouwescience:directory_renamefrom

ptressel:directory_rename

Commits on Feb 6, 2016

Update for AWS EMR 4.x. Thanks to Kevin Kleinfelter, Bruce Weir, Ashley Engelund.
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Commits on Feb 8, 2016

Memory tuning, turn off logging, etc.
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