In "Add to your books" also search your own library (resist duplicates!)

Would be nice if "Add to your books" also searched the user's local library,
and at least counted copies of the book (e.g. "6 of those already in your books").

Right now if you're cataloging, and inadvertently enter a title twice, the first indication is the "duplicate entry" warning.

The only difficulty I see is that Librarything is NOT a source, so would require some major recoding in the background to make this work.