[PATCH 2 of 4] rebase: improve description of --base

[Mads Kiilerich]

# HG changeset patch
# User Mads Kiilerich <madski at unity3d.com>
# Date 1408403576 -7200
#      Tue Aug 19 01:12:56 2014 +0200
# Node ID 78ca134e8f7d682d4296444dc0623591ac4f5db9
# Parent  60e9ba5a82c801eb7df118af93f5c65423deaadd
rebase: improve description of --base

No Mercurial DAG has ever (!) been drawn in a way where 'up to' would apply.

Instead, describe deliberatey vague and informal instead of seemingly precise
but not describing the essentials:
  rebase the tree around the specified changeset without ancestors of dest

diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -52,8 +52,8 @@ def _makeextrafn(copiers):
     [('s', 'source', '',
      _('rebase from the specified changeset'), _('REV')),
     ('b', 'base', '',
-     _('rebase from the base of the specified changeset '
-       '(up to greatest common ancestor of base and dest)'),
+     _('rebase the tree around the specified changeset without '
+       'ancestors of dest'),
      _('REV')),
     ('r', 'rev', [],
      _('rebase these revisions'),