Display Number of Relation Members in the Selection (Relation Editor)
The relation editor displayed the number how many objects in the selection were actual members of the relation. This information was placed inside a tool tip text and went away with r14888. For editing small relations the different background colors in the selection table give this information too.
But for large relations a numeric display for how many objects in the Selection are already members of the relation is needed. It could be placed in the title of the selection part of the dialog.