PathSet & paths, bool flipDirection = false,
bool includeOutputs = false, bool includeDerivers = false);
-/* Return the path corresponding to the output identifier `id' in the
- given derivation. */
-Path findOutput(const Derivation & drv, string id);
-
bool willBuildLocally(const Derivation & drv);
bool substitutesAllowed(const Derivation & drv);