py3: handle opts correctly for rollback

dryrun and force are just check for None, the value is not used. So its better
to leave opts as unicodes as that wont harm us.

mercurial/commands.py

@@ -4618,8 +4618,8 b' def rollback(ui, repo, **opts):'
     if not ui.configbool('ui', 'rollback', True):
         raise error.Abort(_('rollback is disabled because it is unsafe'),
                           hint=('see `hg help -v rollback` for information'))
-    return repo.rollback(dryrun=opts.get('dry_run'),
-                         force=opts.get('force'))
+    return repo.rollback(dryrun=opts.get(r'dry_run'),
+                         force=opts.get(r'force'))
 
 @command('root', [])
 def root(ui, repo):