Underlines gone in single-click mode

[Jeff Waugh <jdub perkypants org>]

Hey gang,

So, I've forced myself to try using single click mode for a while, and found
that recent versions no longer have the mouseover label underlines [1].

The cursor changes into a hand icon, however, so at least there is some
indication that it will operate differently to double-click mode.

I have confused myself a number of times due to this lack of affordance now,
so I wonder what the rationale for changing it was, and if we could bring it
back. I think it might be useful to detect double-click actions too, if
that's feasible.

Thanks,

- Jeff

[1] When you hover your cursor over an icon or label, and underline appears
on the label, rather like the popular a:hover stuff you see in web browsers.

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