check in rootcint for definition of R__B64 so that when Rtypes.h is

processed the correct typedefs are put in the dictionary. Fixes
sizeof(Seek_t) problem in interpreter.


git-svn-id: http://root.cern.ch/svn/root/trunk@6203 27541ba8-7e3a-0410-8455-c3a389f83636