[Rivet] HepMC, cmake and our bootstrap script

[Frank Siegert]

>> I'm coming back to this, since recently (r4100) Andy has updated the
>> HepMC version in the bootstrap script to 2.06.08. Unfortunately,
>> that's a version (as Hendrik noted) which doesn't have ./configure
>> anymore, so our rivet-bootstrap fails right there.
>
> Configure is back in 2.06.09.

Aaah... even better, thanks for pointing that out!

So I'll revert the reversion and update it to 2.06.09, and in the
future whenever we update HepMC versions we'll have to check whether
configure is gone again.

Cheers,
Frank