How to activate gnuplot toolkit?

[Daniel J Sebald]

How does one activate the gnuplot toolkit?  I recall someone writing in 
the maintainers list how to swap back and forth, but I get:

> > set(1,'__graphics_toolkit__', 'gnuplot')
error: set___graphics_toolkit__: invalid graphics toolkit
> > set(1,'__graphics_toolkit__')
error: set: invalid number of arguments

Thanks,

Dan