Updated release notes for hadoop-2.4.1 rc1.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1604315 13f79535-47bb-0310-9956-ffa450edef68
YARN-2187. FairScheduler: Disable max-AM-share check by default. (Robert Kanter via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1604322 13f79535-47bb-0310-9956-ffa450edef68