Consider effect of other plugins

[peterwilsoncc]

Consider running the redirect_canonical filter later to account for other plugins changing the redirect_url.

If another plugin changes the redirect_url, it's possible they are altering the displayed content and this plugin should defer to a 301 redirect.

[peterwilsoncc]

Run filter early to check for original url

Run filter late to check if another plugin has changed the url. Do a 301 if the redirect has changed.