rebase: mention phases in the help

Mention that Mercurial helps you not do what you've just been warned not
to do, with a reference to the 'phases' help topic (not the 'phase'
command help).

Thanks to Pierre-Yves David <[e-mail]> for
motivating this change and Wagner Bruna
<[e-mail]> for advising on how to do it in an
i18n-friendly way.

hgext/rebase.py

@@ -68,6 +68,9 b' def rebase(ui, repo, **opts):'
     same rebase or they will end up with duplicated changesets after
     pulling in your rebased changesets.
 
+    In its default configuration, Mercurial will prevent you from
+    rebasing published changes. See :hg:`help phases` for details.
+
     If you don't specify a destination changeset (``-d/--dest``),
     rebase uses the tipmost head of the current named branch as the
     destination. (The destination changeset is not modified by