Bug#540406: the wxt driver deserves its own package

[Christoph Bersch]

Hi,

I think the current configuration can also confuse users, because the 
names suggest, that only X11 and qt are supported as interactive terminals:

gnuplot-nox:  no interactive terminals
gnuplot-x11: X11 and wxt (wxt is default)
gnuplot-qt: X11, wxt, and qt (wxt is default)

But I have no alternative suggestion.

Christoph