Adding dropTake to RDD. Allows to drop first 'drop' elements and then take next 'take' elements#617

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trulite wants to merge 3 commits intomesos:masterfrom trulite:master

+47

Commits on May 19, 2013

dropTake - drop first drop element and thne take next take elements
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Drop is now accumulated from how many the salves could drop
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Commits on May 20, 2013

More test and corrections
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