convert: add config option to control storing original revision common.commit.__init__ sets saverev=True by default. The side effect of this is that the hg sink will always set the "convert_revision" extras key to the commit being converted. This patch adds a config option to disable this behavior. While most consumers will want "convert_revision" to be a) written b) with the exact Git commit that was converted, some have use cases that prefer otherwise. In my case, I am performing significant rewrites of a Git repository *before* it is fed into `hg convert`. I have to do this because `hg convert` does not easily support the kind of transform I desire, even with extensions. (For the curious, I am "linearizing" the history of a GitHub repo by removing merge commits which add little value to the final history. It isn't easy to do this during `hg convert` because of Mercurial's file copy/rename metadata requirements.) In my scenario, my pre-convert transform stores a "convert_revision" key in the Git commit object containing the original Git commit ID. I want this original Git commit ID carried forward to Mercurial. By disabling the setting of this extra during `hg convert` and copying the value from the Git commit object, I can have the final "convert_revision" extra key contain the original Git commit ID. An added test verifies this exact scenario. This feature could likely be implemented for other VCS sources. But until someone needs the feature, I'm inclined to hold off implementing.

Create a repository:

  $ hg config
  defaults.backout=-d "0 0"
  defaults.commit=-d "0 0"
  defaults.shelve=--date "0 0"
  defaults.tag=-d "0 0"
  devel.all-warnings=true
  largefiles.usercache=$TESTTMP/.cache/largefiles (glob)
  ui.slash=True
  ui.interactive=False
  ui.mergemarkers=detailed
  ui.promptecho=True
  $ hg init t
  $ cd t

Make a changeset:

  $ echo a > a
  $ hg add a
  $ hg commit -m test

This command is ancient:

  $ hg history
  changeset:   0:acb14030fe0a
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     test
  

Verify that updating to revision 0 via commands.update() works properly

  $ cat <<EOF > update_to_rev0.py
  > from mercurial import ui, hg, commands
  > myui = ui.ui.load()
  > repo = hg.repository(myui, path='.')
  > commands.update(myui, repo, rev=0)
  > EOF
  $ hg up null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ python ./update_to_rev0.py
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg identify -n
  0


Poke around at hashes:

  $ hg manifest --debug
  b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644   a

  $ hg cat a
  a

Verify should succeed:

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  1 files, 1 changesets, 1 total revisions

At the end...

  $ cd ..