Now that the new focus architecture has been putback, Philip should reevaluate
the JTable code to see if portions of it can be implemented more effectively.

In particular, we would like to see the dependency on isManagingFocus removed.
We would also like JTable to respond to the traversal keys returned by
Component.getFocusTraversalKeys(int) instead of assuming that the keys are
TAB and SHIFT-TAB. Finally, Philip removed calls to JComponent.
setNextFocusableComponent from JTable in response to BugID 4260718. Because of
this change, when a cell in a JTable is focused and its editor is active (with a
blinking caret) you cannot use the a traversal key to move to the next cell and
activate its editor.