[Rivet] [Fastjet] PseudoJets constructor

[David Grellscheid]

Hi Gavin,

> Initialising the members takes some extra time 

It always does, but does it actually make a measurable difference in any 
realistic situation?

> Having said that, for the next release we're revisiting the decision about 
> default initialisation, so in the future PseudoJet() may well give a 
> sensible object.

Please do that, it would make the behaviour much less surprising, since 
most other non-simple types do default-initialize on construction. The 
theoretical time saving in our case was negligible compared to the 
debugging we just had to do. :-)

Thanks,

   David