When CINT doesn't know the header file of a class, ask TCint to try to...

When CINT doesn't know the header file of a class, ask TCint to try to generate the dictionary nevertheless in case it knows it through TClass.
Fixes issue reported at http://root.cern.ch/phpBB3/viewtopic.php?f=3&t=11597


git-svn-id: http://root.cern.ch/svn/root/trunk@36699 27541ba8-7e3a-0410-8455-c3a389f83636