[CF-metadata] area_fraction

[Jonathan Gregory]

Dear Elke

> I have another question to the other fraction quantities. What will 
> happen to the other standart names:
> 
> vegetation_area_fraction
> land_area_fraction

> You want to define a superior area fraction, with data information
> land_cover= 'vegetation'
> land_cover='land'
> land_cover='forest'

> What will happen to the old standart names just existing?
They will continue to be valid.

Cheers

Jonathan