Add a new static member fgReadInfo and a setter function

void TFile::SetReadStreamerInfo(Bool_t readinfo)
   // static function to set fgReadInfo.
   // If fgReadInfo is true (default) TFile::ReadStreamerInfo is called
   //  when opening the file.
   // It may be interesting to set fgReadInfo to false to speedup the file
   // opening time or in case libraries containing classes referenced
   // by the file have not yet been loaded.
   // if fgReadInfo is false, one can still read the StreamerInfo with
   //    myfile.ReadStreamerInfo();


git-svn-id: http://root.cern.ch/svn/root/trunk@16229 27541ba8-7e3a-0410-8455-c3a389f83636