[Rivet] thrust

[Andrii Verbytskyi]

Dear Andy,
1) recently after looking into the thrust routine in Rivet I've fount
that objects are arranged by |p| and not p_T as in the referenced Pythia
code (line 77228 of pythia6428.f).
In some cases it produces unexpected outputs.
2) The line 
if (axis.x() < 0) axis = -axis;
in the same code looks very suspicious. Is that a bug or a feature?

Best regards,
Andrii