detect reducer skew amounst each job's tasks
save job warnings as job is updated
was using the wrong warning key
include number of skewed reducers as well as the ids of those that are skewed
Put a floor for the threshold value so that one slightly slower reducer doesn't appear skewed if all the other reducers have a tightly coupled execution time.
merge changes from master
Merge pull request #24 from mortardata/mroddy_warn_on_reducer_skew

detect reducer skew in each job's tasks