Invert label background when dragging a file

[humdinger]

This is hrev57243, 64bit.

My Desktop colour is dark, so the icon labels are white.
If you drag an icon over a Tracker window (which usually has a white background) to move the file, the white label becomes practically invisible.

When selecting an icon, the label background is inverted, so the white label text is printed on black. If dragging an icon did the same, it would always be readable.

[Starcrasher]

Since during the time that you drag the icon it is obviously selected; it would make sense if the label was acting the same, indeed.