opStrategy and ordering for ArithmeticPostAgg

Fixes #510
all manners of new tests
removed build section that didn't work (direct from whirr repo); added info on resource files needed to run test; tweaked whirr config section to match current requirements; changed cluster-start section to reflect fact that we're starting multiple instances; other minor edits
Merge branch 'master' into igalDruid
Add HdfsTaskLogs
add toString method for JavascriptDimExtractionFn
Merge pull request #620 from metamx/more-tostring

add toString method for JavascriptDimExtractionFn
Document batch ingestion jobProperties.
Merge pull request #623 from metamx/document-hadoop-jobProperties

Document how to set hadoop properties
More explicit example of jobProperties.
Merge pull request #624 from metamx/better-jobProperties-example

Better example of jobProperties.
fix one of the TODOs and add test case
Merge branch 'master' into more-tests
Merge pull request #604 from metamx/more-tests

All manners of "new" tests
Merge pull request #617 from metamx/igalDruid

Igal druid
Approximate Histogram Module
fix approximate histogram serde to not change buffer limit
Merge pull request #625 from metamx/approx-histo

Approximate Histograms and Quantiles
refactor docs for histograms
make histos work with groupby maybe