TStreamerBase passes the artificial type name "BASE".

(cherry picked from commit 8e89cc0e5c7168c2ae898c61bd1b2b58d2913d87)

Conflicts:
	core/meta/src/TStreamerElement.cxx
Fix comment.

(cherry picked from commit 56bf05c5414849e6bdd8f5b269d03940aa4b6e88)