HADOOP-11254. Changed visibility of AccessControlList to be public for consumption by ecosystem. Contributed by Zhijie Shen.

(cherry picked from commit b18e8a272eaf69d05d567b8c39e3e7c556935b08)
HDFS-7276. Limit the number of byte arrays used by DFSOutputStream and provide a mechanism for recycling arrays.

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSOutputStream.java