MAHOUT-1379: ClusterQualitySummarizer fails with the new T-Digest for clusters with 1 data point

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1551004 13f79535-47bb-0310-9956-ffa450edef68
MAHOUT-1380: Streaming KMeans fails when executed in Sequential Mode

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1551008 13f79535-47bb-0310-9956-ffa450edef68