HDFS-6413. xattr names erroneously handled as case-insensitive. Contributed by Charles Lamb.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2006@1595110 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6414. xattr modification operations are based on state of latest snapshot instead of current version of inode. Contributed by Andrew Wang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2006@1595113 13f79535-47bb-0310-9956-ffa450edef68