histedit: clean abort when there is nothing to edit

histedit: rename `revs` in `ctxs` inside the `between` function The variable content is actually contexts, not revision numbers.

test: fix invalid redirection for histedit text Appending to the file is wrong, we want new content.

vfs: backout fchmod change from 76b73ce0ffac Only works on Unix with Python >= 2.6, need a different fix.

histedit: refuse to edit public changeset Public changeset are immutable. This changeset enforce that in histedit.

histedit: ignores hidden revision when checking for orphaned nodes We do not want hidden revision to block histedit. They are already "dead" and we do not care about dead orphans. see similar changeset 9e2dc0d292cd for rebase.

histedit: simplify computation of edited set (issue3620) This complex code can be replaced by two simple revset calls.

histedit: add obsolete support When the obsolete feature is enabled, histedit creates obsolescence marker instead of stripping replaced changesets. For now, we keep stripping temporary nodes created along the way.

histedit: replace various nodes lists with replacement graph (and issue3582) This changeset rewrites the change tracking logic of histedit to record every operation it does. Tracked operations record the full list of "old" node that will eventually be removed to the list of new nodes that replace it. Operations on temporary nodes are tracked too. Dropped changesets are also recorded as an "old" node replacement by nothing. This logic is similar to the obsolescence marker one and will be used for this purpose in later commit. This new logic implies a big amount of change in the histedit code base. histedit action functions now always return a tuple of (new-ctx, [list of rewriting operations]) The old `created`, `replaced` and `tmpnodes` are no longer returned and stored during histedit operation. When such information is necessary it is computed from the replacement graph. This computation is done in the `processreplacement` function. The `replacemap` is also dropped. It is computed at the end of the command from the graph. The `bootstrapcontinue` methods are altered to compute this different kind of information. This new mechanism requires much less information to be written on disk. Note: This changes allows a more accurate bookmark movement. bookmark on dropped changeset are now move of their parent (or replacement of their parent) instead of their children. This fix issue3582

merge with durin42