Smart API additions

[Anders F Björklund]

Some clarifications: (I'm bad at usecases)

> +    def getSource(self):
> +

PackageKit uses this field to determine
which packages have the same "basename".

> +    def getLicense(self):
> +

PackageKit uses this field to determine
"free" status by looking at the licenses.

> +    def getChangeLog(self):
> +

This is for display in the user interface,
but probably only for installed packages ?

> +    def getBuildTime(self):
> +

This is for smart query, so it can sort by
"latest packages first" for the output...

--anders