ENH: Order vibrations in Ideal gas thermochemistry

A student in our group recently calculated vibrational frequencies with VASP and used ASE's thermochemistry module for calculating the ideal gas free energies. VASP seems to give the free energies ordered from largest to smallest. Thus, the IdealGasThermo class cut the 6 highest vibrational frequencies as it deletes up to 6 of the first vibrations in the list.

I just added two lines to order the given vibrations by magnitude of their real components. I can not think of a physical case where the actual vibrational frequencies are lower in frequency than the translations and rotations.