evolve: don't show working directory obsolete message if we were on it This patch tweaks showing wc obsolete message functionality to not show the message if the operation led us to the same changeset we were on before and it didn't obsoleted it. This make failed updates, update on current changeset and a pull with no change omit showing the message. This has some cons like if you are on rev 1 which is obsolete and you do `hg up <revset>` where revset is some revset which resolves to the rev 1, we won't show the warning as shown earlier.

prev: jump to parent's successor if parent is obsolete and topic is involved `hg stack` shows a linear chain of commits even when they are not linear chain and some changesets are obsoleted and have successors as separate head. This is very nice to have a post evolution view of the stack. However when `hg prev` is run on an unstable changeset whose parent is obsolete and does not topic but parents successor has the topic, it shows no parent on the topic. This patch makes `hg prev` update to parent's successor and make things follow the stack order.