HDFS-4270. Replications of the highest priority should be allowed to choose a source datanode that has reached its max replication limit (Derek Dagit via tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1428883 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-8427. Convert Forrest docs to APT, incremental. (adi2 via tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1428945 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'branch-0.23' of github.com:griddynamics/yhadoop-common into branch-0.23-gd
Merge branch 'branch-0.23-gd' of github.com:griddynamics/yhadoop-common into fb-xxx-hadoop-auth-kerberos-realm-branch-0.23-gd