HADOOP-9450. HADOOP_USER_CLASSPATH_FIRST is not honored; CLASSPATH is PREpended instead of APpended. Contributed by Chris Nauroth and Harsh J. (harsh)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1469214 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