* Garbage collector: don't do a complete topological sort of the Nix

store under the reference relation, since that means that the
  garbage collector will need a long time to start deleting paths.
  Instead just delete the referrers of a path first.

src/libstore/local-store.hh

@@ -143,6 +143,10 @@ private:
     
     void upgradeStore12();
 
+    void tryToDelete(GCAction action, const PathSet & livePaths,
+        const PathSet & tempRootsClosed, PathSet & done, PathSet & deleted,
+        const Path & path, unsigned long long & bytesFreed);
+    
 };