TabContainer: TabButton loses hover effect after mouse has been over close icon

[bill]

In test_TabContainer.html, move your mouse over a tab, then over the tab's close icon, and then back over the main part of the tab.

The tab loses it's dijitTabHover class, thus losing the coloring that should be there (since the mouse is still over the tab).

[bill]

Bug is that FormWidget._onMouse() is responding to the onmousleave event on the *close icon* and thinking that the entire tab has lost focus.

A complication from the stateModifier code that tries to affect the class of the widget's domNode in response to changes on inner nodes (in this case, the icon).

[bill]

(In [16026]) Refactor TabButton? so that hovering over the close icon only affects the class of the closeButton node, not TabButton?.domNode. This fixes #8245: TabButton? loses hover effect after mouse has been over close icon.

Also removed unneeded CSS from dijit.css, and used JS set .closeNode-hover class name, rather than :hover, which doesn't work in IE except on an <a>.

!strict

[bill]

(In [16030]) Remove old references to dijitTabCloseButtonHover; leftover work from [16026]. Refs #8245.