Performance: Swing drop locations should override equals

JList, JTable, JTree, JTextComponent fire a property change to indicate when there is a change to the drop location. Right now, these notifications are sent out repeatedly during DnD, even if the mouse isn't moved and the real location hasn't changed. This can be expensive if each change triggers a repaint or some other action.

PropertyChangeSupport is designed to only send notifications if the value is actually changed, but to take advantage of this, DropLocations need to override equals().

And to be correct, they should also override hashCode().