Added 2nd virial coeff. functions
Added 2nd virial coeff. functions

SasView/sasview,SasView/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,SasView/sasview,lewisodriscoll/sasview,SasView/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview