HDFS-573: Windows builds will require CMake

FYI, I plan to commit HDFS-573 next week, which ports libhdfs to Windows. With this patch, we have a new build requirement: Windows build machines now require CMake. I've updated BUILDING.txt accordingly. For those of you working on a Windows dev machine, please install CMake at your earliest co

Jenkins build is back to normal : Hadoop-Yarn-trunk #632

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