Support versions enumeration

[ony]

Since range of versions can be represented as an enumeration of intermediate version it is possible to represent them within current Paludis dependencies format.
Moreover some packages declare their dependencies like "==1.1.* || ==1.0.* || ==0.11.* but asVersionIntervals re-organize them in ranges like >=0.11 && <0.12, >=1.0 && <1.2 effectively causing exception about unsupported version.