Add warning for old and redirected Curse URLs

[amas0]

During Curse updating, addon URLs are accessed to check for any URL redirection that may occur on Curse's end. This can occur when a user has specified an old URL for their addon, such as for a since-renamed addon.

While these addons update correctly, it could be useful to warn the users that they are using an out-of-date specification to encourage them to update the specification.

[amas0]

Did some poking on this for a little and had a thought -- is there any reason why we wouldn't want to automatically update a user's addons.txt and installed.ini with the proper URL if its detected as redirected or out of date?

[grrttedwards]

is there any reason why we wouldn't want to automatically update a user's addons.txt and installed.ini with the proper URL if its detected as redirected or out of date?

@amas0 Hey. Yeah I guess I never thought about this. I think this could be a decent improvement, but I think it's a pretty infrequent occurrance, and doesn't really save a round trip (since every URL is checked, like you added), so I might not go out of my own way to implement such a thing.

Still open to PR's of course!