* Allow unprivileged users to run the garbage collector and to do

`nix-store --delete'.  But unprivileged users are not allowed to
  ignore liveness.
* `nix-store --delete --ignore-liveness': ignore the runtime roots as
  well.

src/libstore/local-store.hh

@@ -66,6 +66,9 @@ public:
     void syncWithGC();
 
     Roots findRoots();
+
+    void collectGarbage(GCAction action, const PathSet & pathsToDelete,
+        bool ignoreLiveness, PathSet & result, unsigned long long & bytesFreed);
 };