Regression/side effect from rBA9448cef00d1b3, while we do want to get
one Blender object per 'o' line (object declaration) in OBJ file, we do
want to 'reuse' same objects when same OBJ groups ('g' lines) are used
inside of a same object, in case we split OBJ groups into objects...

Thanks to Jacques Lucke (@JacquesLucke) for initial investigation.