HADOOP-12451. Setting HADOOP_HOME explicitly should be allowed. (kasha)

(cherry picked from commit db145e0c9add81c74d853baa8187005f97ea1b53)

Conflicts:
	hadoop-common-project/hadoop-common/src/main/bin/hadoop-config.sh

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -40,6 +40,8 @@ Release 2.7.2 - UNRELEASED
 
     HADOOP-12213. Interrupted exception can occur when Client#stop is called.
     (Kuhu Shukla via ozawa)
+    
+    HADOOP-12451. Setting HADOOP_HOME explicitly should be allowed. (kasha)
 
 Release 2.7.1 - 2015-07-06 
 

hadoop-common-project/hadoop-common/src/main/bin/hadoop-config.sh

@@ -250,8 +250,11 @@ TOOL_PATH="${TOOL_PATH:-$HADOOP_PREFIX/share/hadoop/tools/lib/*}"
 
 HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.dir=$HADOOP_LOG_DIR"
 HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.file=$HADOOP_LOGFILE"
-HADOOP_HOME=$HADOOP_PREFIX
-if $cygwin; then
+
+if [ "$HADOOP_HOME" = "" ]; then
+  HADOOP_HOME=$HADOOP_PREFIX
+fi
+if [ "$cygwin" = true ]; then
   HADOOP_HOME=$(cygpath -w "$HADOOP_HOME" 2>/dev/null)
 fi
 export HADOOP_HOME