cmdutil: introduce 'editform' to distinguish the purpose of commit text editing

This information will be used to switch '[committemplate] changeset'
definition according to its purpose in the subsequent patch.

This information also makes it easier to hook commit text editing only
in the specific cases.
fetch: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, COMMAND and ROUTE are omitted.
gpg: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, 'sign' is used as COMMAND, and ROUTE is omitted.
histedit: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes for COMMAND

In this patch:

  - 'edit', 'fold', 'mess' and 'pick' are used as COMMAND
  - ROUTE is omitted

'histedit.pick' case is very rare, but possible if:

  - target revision causes conflict at merging (= requires '--continue'), and
  - description of it is empty ('hg commit -m " "' can create such one)

In the code path for 'histedit --continue' (the last patch hunk),
'canonaction' doesn't contain the entry for 'fold', because 'fold'
action causes:

  - using temporary commit message forcibly, and
  - making 'editopt' False always (= omit editor invocation if commit
    message is specified)
mq: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch:

  - MQ command names (qnew/qrefresh/qfold) are used as COMMAND
  - ROUTE is omitted
rebase: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch:

  - COMMAND is omitted
  - 'normal' and 'collapse' are used as ROUTE
shelve: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch:

  - 'shelve' is used as COMMAND
  - ROUTE is omitted
transplant: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  EXTENSION[.COMMAND][.ROUTE]

  - EXTENSION: name of extension
  - COMMAND: name of command, if there are two or more commands in EXTENSION
  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, COMMAND and ROUTE are omitted.
backout: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, ROUTE is omitted..
graft: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, ROUTE is omitted.
tag: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, 'add' and 'remove' are used as ROUTE
commit: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, 'normal' and 'amend' are used as ROUTE.
import: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, 'normal' and 'bypass' are used as ROUTE.
cmdutil: look commit template definition up by specified 'editform'

Before this patch, '[committemplate] changeset' definition is shared
between all actions invoking 'commitforceeditor()'.

This prevents template definition from showing action specific
messages: for example, 'hg tag --remove' may need specific
message to call attention, but showing it may be redundant for
other actions.

This patch looks commit template definition up by specified
'editform' introduced by prior patches. 'editform' are
dot-separated list of names, and treated as hierarchical one.
cmdutil: use '[committemplate]' section like as map file for style definition

Before this patch, each template definitions for 'changeset*' in
'[committemplate]' section have to be written fully from scratch,
even though many parts of them may be common.

This patch uses '[committemplate]' section like as the map file for
the style definition. All items other than 'changeset' can be referred
from others.

This can reduce total cost of template customization in
 '[committemplate]' section.

When the commit template other than '[committemplate] changeset'
is chosen by 'editform', putting '[committemplate] changeset'
value into the cache of the templater causes unexpected result,
because the templater stores the specified (= chosen) template
definition into own cache as 'changeset' at construction time.

This is the reason why '[committemplate] changeset' can't be referred
from others.
push: extract future heads computation into pushop

Bundle2 will allow pushing all different parts of the push in a single bundle.
This mean that the discovery for each part needs to be done before trying to
push. Currently we may have different behaviors for phases and obsolescence markers
when the push of changesets fails. For example, information may still be
exchanged for a part of the history where changesets are common but where
phases mismatch. So the preparation of the push need to determine what
information need to be pushed in both situations. And it needs a different set of
heads for this. Therefore we are moving heads computation within pushop for easy
access by all parties. We start with the simplest set of heads.

--HG--
extra : amend_source : 1dce65aa35eda368d17454cca28486ece8fe734b
push: extract fallback heads computation into pushop

Similar motivation to `futureheads`, we extract the computation into pushop
to make it available early to all possibly interested parties.

--HG--
extra : amend_source : d3f45636c266b9b1ca0f292f8f5d59b141ac82dc
push: move common heads computation into pushop

Now that both options (push succeed or fall back) live in pushop, we
can move the common heads computation there too. It is a very commonly
accessed attribute so it makes a lot of sense to have it in pushop.
push: rework the bundle2partsgenerators logic

Instead of a single list of functions, we now have a list of names and
a mapping of names to functions. This simplifies wrapping of steps
from extensions. In the same move, declaration becomes decorator-based
(syntax sugar, nom nom nom!).
push: make discovery extensible

We need to gather all discovery before the unified bundle2 push. We
use the same pattern as bundle2 parts generation.