Redmine

I will check.

http://mercurial.selenic.com/wiki/UpgradingMercurial#Upgrading_and_downgrading_repository_formats

1. For compatibility with hg < 1.7 (Nov 2010): 'hg clone --config format.dotencode=False --pull'
2. For compatibility with hg < 1.1 (Dec 2008): 'hg clone --config format.usefncache=False --pull'
3. For compatibility with hg < 0.9.4 (Jun 2007): 'hg clone --config format.usestore=False --pull'

r4676 is great idea.
I confirmed source:trunk/test/fixtures/repositories/mercurial_repository.hg@4676 is compatible with Mercurial 1.0.

$ hg clone -U http://selenic.com/repo/hg hg-stable
$ cd hg-stable
$ hg update 1.0
$ make local
$ LANG=C ./hg --version
Mercurial Distributed SCM (version 1.0)

$ LANG=C /somewhere/hg-stable/hg unbundle ../mercurial_repository.hg 
/somewhere/hg-stable/mercurial/demandimport.py:46: DeprecationWarning: the sha module is deprecated; use the hashlib module instead
  mod = _origimport(head, globals, locals)
adding changesets
adding manifests
adding file changes
added 17 changesets with 24 changes to 13 files (+2 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)

I confirmed that Mercurial 1.0 can access this repository.

$ cat .hg/requires 
revlogv1
store

$ LANG=C /somewhere/hg-stable/hg tip
changeset:   16:4cddb4e45f52
tag:         tip
parent:      6:7fab6ce80d87
user:        jsmith <jsmith@foo.bar>
date:        Sat Jan 01 00:00:00 2000 +0900
summary:     Added tag tag-init-revision for changeset 0885933ad4f6