Panic if the return value from the closure passed to Object::connect() returns a value of the wrong type
Panic if the return value from the closure passed to Object::connect() returns a value of the wrong type

Or no value at all if a return value is needed, or a value if no return
value is needed.

By previously silently ignoring type errors here, hard to debug problems
appeared when code didn't get any meaningful return values.

rust-gnome/glib,EPashkin/rust-gnome-glib