rebase: suggest help -e histedit

Users unfamiliar with an extension should be reading the
documentation for the feature, not the command.

hgext/rebase.py

@@ -217,7 +217,7 b' def rebase(ui, repo, **opts):'
         keepopen = opts.get('keepopen', False)
 
         if opts.get('interactive'):
-            help = "hg help histedit"
+            help = "hg help -e histedit"
             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 histedit")
+  abort: interactive history editing is supported by the 'histedit' extension (see "hg help -e histedit")
   [255]
 
   $ hg rebase --interactive
-  abort: interactive history editing is supported by the 'histedit' extension (see "hg help histedit")
+  abort: interactive history editing is supported by the 'histedit' extension (see "hg help -e histedit")
   [255]
 
   $ cd ..