HDFS-5363. Refactor WebHdfsFileSystem: move SPENGO-authenticated connection creation to URLConnectionFactory. Contributed by Haohui Mai.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1535169 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5341. Reduce fsdataset lock duration during directory scanning. Contributed by Qus-Jiawei.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1535188 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4312-trunk-gd