rebase: factor out histedit help command

hgext/rebase.py

@@ -217,8 +217,9 b' def rebase(ui, repo, **opts):'
         keepopen = opts.get('keepopen', False)
 
         if opts.get('interactive'):
+            help = "hg help histedit"
             msg = _("interactive history editing is supported by the "
-                    "'histedit' extension (see \"hg help histedit\")")
+                    "'histedit' extension (see \"%s\")") % help
             raise util.Abort(msg)
 
         if collapsemsg and not collapsef: