[Rivet] HepMC, cmake and our bootstrap script

[Hendrik Hoeth]

Thus spake Hendrik Hoeth (hendrik.hoeth at cern.ch):

> Shall we rely on the existence of cmake?

It seems this is now becoming Grid requirement and will be installed by
default, so we can rely on it in the future.

-- 
Man is the best computer we can put aboard a spacecraft, and
the only one that can be mass produced with unskilled labor.
                                        -- Wernher von Braun