• Vectors/HepMCTraits.h, Vectors/HepMCConverter.*: Introduced

units for HepMC. By includeing GenEvent.h and checking if the
Units.h file also was included, the default behavior of the traits
class should be correct. (herwig:ticket:202)

• Config/Unitsystem.h: Added centimeter which may be used as a

unit in HepMC.