Merge commit '75bf97b57539e5572e7ae8eba72bac6562c63c07'

Conflicts:
	subtree/rabit/rabit-learn/io/line_split-inl.h
	subtree/rabit/yarn/build.sh

subtree/rabit/rabit-learn/io/io.h

@@ -19,6 +19,7 @@ namespace rabit {
  * \brief namespace to handle input split and filesystem interfacing
  */
 namespace io {
+/*! \brief reused ISeekStream's definition */
 typedef utils::ISeekStream ISeekStream;
 /*!
  * \brief user facing input split helper,