Implement forward declared classes, so autoloading is not triggered for ptr to class. tagnum setup is done via new API func G__get_linked_tagnum_fwd().
Reduce the number of unnecessary fopens (work-around mavc8 runtime lib bug)
Initialize G__srcfile.breakpoint
Passes all roottests except for ./root/meta/evolution/foreign


git-svn-id: http://root.cern.ch/svn/root/trunk@18099 27541ba8-7e3a-0410-8455-c3a389f83636