HepMC2-2.06.09-bp150.2.4

- Trim description for size (like was already done for HepMC
  1st Generation).

- Fix shared lib Group, should be System/Libraries.

- Add explicit Conflicts between HepMC2-devel and HepMC-devel > 3,
  make HepMC2-devel provide HepMC-devel = %{version}.

- Adapt to using HepMC2 as package name.

- Initial version (copy from HepMC = 2.06.09).