rebase: enable histedit for useful help with it

hgext/rebase.py

@@ -217,7 +217,12 b' def rebase(ui, repo, **opts):'
         keepopen = opts.get('keepopen', False)
 
         if opts.get('interactive'):
-            help = "hg help -e histedit"
+            try:
+                if extensions.find('histedit'):
+                    enablehistedit = ''
+            except KeyError:
+                enablehistedit = " --config extensions.histedit="
+            help = "hg%s help -e histedit" % enablehistedit
             msg = _("interactive history editing is supported by the "
                     "'histedit' extension (see \"%s\")") % help
             raise util.Abort(msg)

tests/test-rebase-parameters.t

@@ -490,11 +490,11 b' Test --tool parameter:'
   saved backup bundle to $TESTTMP/b3/.hg/strip-backup/e4e3f3546619-b0841178-backup.hg (glob)
 
   $ hg rebase -i
-  abort: interactive history editing is supported by the 'histedit' extension (see "hg help -e histedit")
+  abort: interactive history editing is supported by the 'histedit' extension (see "hg --config extensions.histedit= help -e histedit")
   [255]
 
   $ hg rebase --interactive
-  abort: interactive history editing is supported by the 'histedit' extension (see "hg help -e histedit")
+  abort: interactive history editing is supported by the 'histedit' extension (see "hg --config extensions.histedit= help -e histedit")
   [255]
 
   $ cd ..