Squashed 'subtree/rabit/' changes from d558f6f..091634b

091634b fix

git-subtree-dir: subtree/rabit
git-subtree-split: 091634b259

src/allreduce_base.h

@@ -65,7 +65,7 @@ class AllreduceBase : public IEngine {
   }
   /*! \brief whether is distributed or not */
   virtual bool IsDistributed(void) const {
-    return tracker_uri == "NULL";
+    return tracker_uri != "NULL";
   }
   /*! \brief get rank */
   virtual std::string GetHost(void) const {