[Rivet] normalising histograms

[Emily Nurse]

Dear Rivet routine writers,

I have changed the vetoEvent() functionality for routines, such that  
it no longer affects the sumOfWeights() function. This function now  
sums the weights of all events from the generator, not just those that  
pass certain cuts. This is because many analyses were normalising  
histograms using sumOfWeights() but assuming that it really did sum  
all the weights, more information is here:

http://projects.hepforge.org/rivet/trac/ticket/250

Can everyone check that their routines are now  doing the correct  
thing when normalising the histograms? Its quite possible that some  
are still not normalising correctly.

Thanks,
Emily.