* Garbage collector: added an option `--use-atime' to delete paths in

order of ascending last access time.  This is useful in conjunction
  with --max-freed or --max-links to prefer deleting non-recently used
  garbage, which is good (especially in the build farm) since garbage
  may become live again.

  The code could easily be modified to accept other criteria for
  ordering garbage by changing the comparison operator used by the
  priority queue in collectGarbage().

src/libstore/store-api.cc

@@ -14,6 +14,7 @@ GCOptions::GCOptions()
     ignoreLiveness = false;
     maxFreed = ULLONG_MAX;
     maxLinks = 0;
+    useAtime = false;
 }