add detailed comment about gbmcore

utils/xgboost_stream.h

@@ -9,7 +9,9 @@
  */
 namespace xgboost{
     namespace utils{
-        /*! \brief interface of stream I/O, used to serialize model */
+        /*! 
+         * \brief interface of stream I/O, used to serialize model 
+         */
         class IStream{
         public:
             /*! 

utils/xgboost_utils.h

@@ -51,7 +51,8 @@ namespace xgboost{
         inline void Warning( const char *msg ){
             fprintf( stderr, "warning:%s\n",msg );
         }
-        /*! \brief replace fopen, report error when the file open fails */        
+
+        /*! \brief replace fopen, report error when the file open fails */
         inline FILE *FopenCheck( const char *fname , const char *flag ){
             FILE *fp = fopen64( fname , flag );
             if( fp == NULL ){