pop09 output: definition of calculated properties.

The following symbols have been used to define the calculated properties:

1. Ω_i: basin labelled by i
2. ρ(r): spinless electron density.
3. ρ^α(r): α-spin electron density.
4. ρ^β(r): β-spin electron density.
5. π(r, r′): spinless electron pair density.
6. π^αβ(r, r′): αβ contribution to electron pair density.
7. π^αα(r, r′): αα contribution to electron pair density.
8. π^ββ(r, r′): ββ contribution to electron pair density.