[Rivet] Transverse Mass for WFinder

[Gavin Hesketh]

Hi,
the WFinder in Rivet currently allows you to set a min and max mass. 
These should (in 99% of W analyses) be cuts on the transverse mass, not 
the full invariant mass.
Can these mass cuts be changed by default to operate on the transverse 
mass? Or add some flag to the WFinder to switch between transverse and 
full mass? Or even just add the transverse mass as a method for the 
InvariantMassFinalState?

cheers,
	Gavin