Periodically re-check a link in case of a change in destination

[dentistformyeye]

I accidentally used unshort.link with a short link that I mistakenly thought I'd already created. After creating the short link, I tried checking the link with unshort.link again, but unshort.link still remembered the old result. After a few days have passed unshort.link should re-check a link rather than output a cached result.

[simonfrey]

Nice idea. I think we already have that info in the db, so should be a small fix.