run-test: restore the -i prompt by write .err before checking if it exists

The `--interactive` flag workis by overwriting the original test file by its
`.err` version. So we need to write it before calling `self.fail`. Otherwise the
`.err` file does not exists and `--interactive` is ignored.

We can move that block code around because it is dedicated to write changed
output and we moves it in the try-except dedicated to handling changed output.

Note that the flog is still badly broken after this change. But at least it crash
instead of being ignored.
run-test: fix AttributeError in the --interactive prompt

One must choose between ``"y yes".split()`` and ``('y', 'yes')``. I choose the
later.

The feature still crash when you answer "yes" to use it. But at least, the
prompt itself works.
run-tests: fix --interactive option

``TTest._testpath`` never existed. This must be the remain of some contributors
side refactoring.
merge: change priority / ordering of merge actions

The ordering of actions matters. Normal file system semantics is that files
have to be removed before a directory with the same name can be created.

Before the first ordering key was to have 'r' and 'f' actions come first,
secondary key was the filename.

Because of future refactorings we want to consistently have all action types
(with a sensible priority) as separate first keys. Grouped by action type, we
sort by filename.

Not processing in strict filename order could give worse performance,
especially on spinning disks. That is however primarily an issue in the cases
where "all" actions are of the same kind and will be grouped together anyway.
merge: move constant assignments a bit and use them more
merge: change debug logging - test output changes but no real changes

Preparing for action list split-up, making sure the final change don't have any
test changes.

The patch moves debug statements around without really changing anything.
Arguably, it temporarily makes the code worse. The only justification is that
it makes it easier to review the test changes ... and in the end the big change
will not change test output at all.

The changes to test output are due to changes in the ordering of debug output.
That is mainly because we now do the debug logging for files when we actually
process them. Files are also processed in a slightly different but still
correct order. It is now primarily ordered by action type, secondarily by
filename.

The patch introduces some redundancy. Some of it will be removed again, some of
it will in the end help code readability and efficiency. It is possible that we
later on could introduce a "process this action list and do some logging and
progress reporting and apply this function".

The "preserving X for resolve" debug statements will only have single space
indentation. It will no longer have a leading single space indented "f: msg ->
m" message. Having this message double indented would thus no longer make
sense.

The bid actions will temporarily be sorted using a custom sort key that happens
to match the sort order the simplified code will have in the end.
merge: separate worker functions for batch remove and batch get

The old code had one function that could do 2 different things. First,
is was called a bunch of times to do one thing. Next, it was called a
bunch of times to do the other thing. That gave unnecessary complexity
and a dispatch overhead. Having separate functions is "obviously" better
than having a function that can do two things, depending on its parameters.
It also prepares the code for the next refactorings.
localrepo: move symlink logic to workingctx
localrepo: improve dirstate.normal lookup by cacheing the function
localrepo: factor out parentworking logic for comparing files

We will temporarily call a private method of the context class while we are in
the process of removing the need of having localrepo.status.
committablectx: move status to workingctx

This method was accidentally placed into the committablectx class. It contains
logic for querying the dirstate so we move it to the correct class.
context: add private _dirstatestatus method

This patch is a step forward in getting rid of needing to check 'parentworking'
throughout the status method. Eventually, we will use the power of inheritance
to do the correct thing when comparing the working directory with its parent.

This method is mostly a copy from localrepo.status. The custom status method of
workingctx will eventually be absorbed by the refactoring of localrepo.status
to context.status but unfortunately we can't do it in one step.
workingctx: call _dirstatestatus in status

Rip out the call from workingctx.status to localrepo.status.
localrepo: call _dirstatestatus instead of duplicating logic
subrepo: add shortid() method to subrepo classes

This method takes an "id" (e.g. a revision id) and returns a "short" version
(e.g. a short revision id).

This will be used on the next revision to fix a small bug in the way that the
text on the promptchoice shown when a subrepo diverges is generated.
subrepo: use subrepo shortid method to generate subrepo diverged promptchoice

We were always using only the first 12 characters of the subrepo revision id
when generating the "subrepo diverged" promptchoice. This is not necessarily
correct for non mercurial subrepos.
help: add additional information in the merge-tools section of config help

The merge tool configuration in general has always been a confusing topic for
user. We add mention of:
- possible pre-existing configuration,
- way to look at it,
- the more detailed help topic about how merge-tools configuration works.

This should help users find they way.
doc: improves merge-tools example with an overwrite of existing config

We highlight the fact that a user hgrc can overwrite the system wide
preconfiguration. As other benefit we show priority value other than 1 and shows
vimdiff configuration is usually directly available. This is valuable as vimdiff
is (surprisingly) a common request from user.
update: when deactivating a bookmark, print a message

This helps prevent user confusion when innocent-seeming commands like
'hg update -C .' are run.
cmdutil: introduce "getcommiteditor()" to simplify code paths to choose editor

"getcommiteditor()" can simplify code paths to choose commit editor
according to '--edit' option as below:

    before:
        editor = cmdutil.commiteditor # or editor = None/False
        if opts.get('edit'):
            editor = cmdutil.commitforceeditor

    after:
        editor = cmdutil.getcommiteditor(**opts)

"getcommiteditor()" accepts option arguments not in "opts" style but
in "**opts" style, because some code paths want to invoke it with just
explicit "edit=True" argument (building dictionary is redundant).