Remove a left-over log statement
Add a grab cursor while drag-scrolling
Make the exclusive-dragging behavior locking

For the left pane, we use an exclusive behavior where you can
grab-scroll left/right or up/down but not both at once. Make this
"lock" once more than 10 pixels have been scrolled in one direction
or the other to prevent weird jumping behavior if the user drifts
off diagonally.