[Rivet] plotting of multi-weight curves in 3.0.0alpha1

[Frank Siegert]

Hi Chris,

> this is to overwrite properties for specific histograms in a local file, no?

Not necessarily, you could also use .* for the file, couldn't you?
I also haven't used it in a while, but I remember it as a way to
overwrite properties for individual histograms, instead of plots, and
since linecolor/style is a histo property and not a plot property I
thought this might work?

> Besides, as far as I can tell this doesn’t work with the
> /path/name[variation] syntax used in v3.0.0alpha1 (at least I couldn’t get
> it to work).

As Andy mentioned, you might just have to be careful to build the
regexp correctly, in particular including those square brackets?

Cheers,
Frank