rebase: suggest the correct tool to continue (not rebase)

Suggest committing (or whatever the current activity is), via
wrongtooltocontinue which uses howtocontinue.

hgext/rebase.py

@@ -915,7 +915,7 b' def restorestatus(repo):'
     except IOError as err:
         if err.errno != errno.ENOENT:
             raise
-        raise error.Abort(_('no rebase in progress'))
+        cmdutil.wrongtooltocontinue(repo, _('rebase'))
 
     if keepbranches is None:
         raise error.Abort(_('.hg/rebasestate is incomplete'))

tests/test-rebase-parameters.t

@@ -481,6 +481,10 b' Test --tool parameter:'
   $ hg resolve -m c2
   (no more unresolved files)
   continue: hg rebase --continue
+  $ hg graft --continue
+  abort: no graft in progress
+  (continue: hg rebase --continue)
+  [255]
   $ hg rebase -c --tool internal:fail
   rebasing 2:e4e3f3546619 "c2b" (tip)
   note: rebase of 2:e4e3f3546619 created no changes to commit