Use javaPathHelper for setting default JAVA_CMD

Index: bin/lein
--- bin/lein.orig
+++ bin/lein
@@ -415,6 +415,8 @@ else
     fi
 fi
 
+export JAVA_CMD=$(javaPathHelper -c leiningen)
+
 if [ ! -x "$JAVA_CMD" ] && ! type -f java >/dev/null
 then
     msg "Leiningen couldn't find 'java' executable, which is required."
