tables: class for active rows (on hover/mouse-over)

[FND]

Here's a patch (code courtesy of Saq) for assigning a class to active table rows (i.e. rows under the mouse pointer). This works similarly to tiddlers' .selected class.

The code is very lightweight (only three additional lines - whereas one is just refactored existing code), so the costs/benefits ratio is very positive.

There's also no noticeable performance impact (I've tested this with an elaborate table).

[FND]

link: discussion on [twdev]

[JeremyRuston]

Fixed in changeset:2770

(The CSS class was changed to "hoverRow" for consistency with CSS terminology)