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

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

hgext/histedit.py

@@ -279,7 +279,7 b' class histeditstate(object):'
         except IOError as err:
             if err.errno != errno.ENOENT:
                 raise
-            raise error.Abort(_('no histedit in progress'))
+            cmdutil.wrongtooltocontinue(self.repo, _('histedit'))
 
         if state.startswith('v1\n'):
             data = self._load()

tests/test-histedit-arguments.t

@@ -133,6 +133,11 b' temporarily.'
   (hg histedit --continue to resume)
   [1]
 
+  $ hg graft --continue
+  abort: no graft in progress
+  (continue: hg histedit --continue)
+  [255]
+
   $ mv .hg/histedit-state .hg/histedit-state.back
   $ hg update --quiet --clean 2
   $ echo alpha >> alpha