Bug#711139: gnuplot-qt: the grid doesn't work with the 'qt' terminal in -persist state

[sfeam]

> Then if I type "quit" to get the prompt back, the window 
> persists as required, but grid button no longer works.

You are trying to use "persist" for something beyond what
it was intended for.   

Yeah - if you type "quit" the program quits and then you
can't make any new plots.  Since zooming or grid generation
or various other things require recalculating the plot, 
it won't work once you quit.

Now it is true that some terminal types are smart enough
to toggle the grid on/off even in persistent mode after
the main program has exiting.   It would be possible to
make qt do that also, but only if the original plot already
contained a grid.  And that is only possible because it 
isn't really necessary to regenerate the whole plot just
to make the grid lines [in]visible.  It doesn't change
the basic limitation.    If toggling the grid is important
to you by itself, could you please file a feature request
for uniform support to toggle it off in terminals that
support a persistent mode?   It would be easy in qt, but
I'd have to think about the other terminals.

	Ethan (sfeam) - upstream devel team