Forum has link dupes

[LogicParrot]

Why this is harmful:

• Confuses search engine crawlers. At best, we'll get double links in search results, at worst, some search engine will suspect we're doing something fishy and decrease our rank.
  
• Confuses a browser's cache, making it download the same content twice if visited from two different links.
  
• Confuses reverse proxies'
  
• Confuses humans.
  
• Messes up hyperlink colors.
  
• Messes up analytics.
  
• Makes mass regex replacements harder.
  
• Makes site scrapers/archivers download many redundant pages. (What if I want an offline backup of the forum so that I can read it in some remote area). We should probably fix this before the [url=https://web.archive.org/web/*/forum.cuberite.org[Internet Archive[/url] starts archiving this site.
  
• There are probably many more issues that I have not considered.