topics: add some noise to rewrittent changeset to prevent hash cycle If we have a changeset with topic `x`, we change it's topic to `y`, fine. When we change it's topic back again to `x`, we get the hash of the the obsoleted changeset which had the topic `x` initially. The same happens for few more cases like clearing the topic of a changeset which initially had no topic. This approach is influenced from cmdutil.amend and other commands (rebase, histedit, etc…)

topic-change: update the working copy along when changing topic of '.' This avoids leaving the working copy behind, removing another large parts of issue5441.

topic-change: cleanup the locking and transaction mechanism The previous code did not garanted we would release all lock (and was a bit more complicated than needed.

topics: use a dict for successors of changesets produced by topic change This patch adds a dictionary to store the successors of changesets which got obsoleted when we change it's topic. This is an improvement in the fix for issue5441.

topic: further simplify the clear logic We just set 'topic' to None and the rest should follow.

topics: drop the clean argument from _changetopics() After this commit, None will represent that we want to clean the topic.

topics: rename '--change' flag to '--rev' flag The --change flag was used to read a revset of which topic should be changed. In mercurial we use --rev for this type of flag. Now things will work as follows: `hg topics topicname`: It will set the current topic `hg topics topicname --rev revset`: Change topic of all the revs in the revset to topicname Further patches will try to achieve the following: `hg topics --clear --rev revset`: clear topic from all the revisions in the revset `hg topics --clear`: clear the current topic (Current behavior) `hg topics --rev revset`: show topics on the revisions in the revset