util: implement a deterministic __repr__ on sortdict `hg debugbundle` is calling repr() on bundle2 part params, which are now util.sortdict instances. Unfortunately, repr() doesn't appear to be deterministic for util.sortdict. So, we implement one. We include the type name because that's the common convention for __repr__ implementations. Having the type name in `hg debugbundle` is a bit ugly. But it's a debug command and I don't care enough to fix it.