added .DS_Store to gitignore for pushes from mac
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mahout
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mahout
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mahout
MAHOUT-1578 Optimizations in matrix serialization (ssc) closes apache/mahout#16
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mahout
MAHOUT-1464 Cooccurrence Analysis on Spark (pat) closes apache/mahout#12