Platform specific warning with F.EVENTNUMBER

A platform specific warning is issued when using F.EVENTNUMBER(odin) functor.

Tuple                               WARNING FunTupleBase<Gaudi::NamedRange_<std::vector<LHCb::Particle const*,std::allocator<LHCb::Particle const*> >,__gnu_cxx::__normal_iterator<LHCb::Particle const* const*,std::vector<LHCb::Particle const*,std::allocator<LHCb::Particle const*> > > > >:: Tuple 'DecayTree' 'unsigned long' has different sizes on 32/64 bit systems. Casting 'EVENTNUMBER' to 'unsigned long long'

I think the fix should be high up (either in Rec or LHCb where ODIN.h is). Putting this issue for here now and will move.

FYI: @peilian