Initial temperatures in critical point calculations of mixtures.

[Gernot Bauer]

For some equations of state, the initial temperatures are problematic. E.g. for model fluids such as LJ fluids with somewhat sensible parameters critical points can be around 100 Kelvin. For pure substances this is not as much of a problem, since we can provide initial estimates. For binary mixtures, this is not possible. We should either make initial guesses more robust or provide ways to allow initial estimates as input.