Using admin_views module causes access denied in migrate ui

When using the admin_views module, admin/content is over-written with a view and uses the 'views_access' method as an access callback.

migrate_ui uses the path 'admin/content/migrate' and doesn't specify the access callback, so it defaults to the menu item above it which uses 'views_access' and causes migrate_ui to always get access denied.

I think admin_views should probably be updated to provide provisions for modules that expect admin/content to be unmolested, but a fix can also be made here by adding 'access callback' => 'user_access'.