Remove domain and protocol from links pointing back to the site.

This avoids having links in the various user-generated contents pointing
to the other version of the website, hence causing a protocol switch to
the visitor.

https://linuxfr.org/suivi/gestion-des-liens-vers-http-s-linuxfr-org

lib/lfmarkdown.rb

@@ -36,6 +36,7 @@ def to_html
     process_internal_wiki_links
     process_wikipedia_links
     ret = fix_heading_levels(super)
+    ret = fix_internal_links(ret)
     ret = process_code(ret)
     ret = add_toc_content(ret) if text.length > 5_000
     ret
@@ -63,6 +64,11 @@ def fix_heading_levels(str)
     str
   end
 
+  def fix_internal_links(str)
+    str.gsub!(/(href|src)="https?:\/\/#{MY_DOMAIN}\//) { |_| "#{$1}=\"/" }
+    str
+  end
+
   # Code taken from gollum (http://github.com/github/gollum)
   def extract_code
     @text.gsub!(/^``` ?(.+?)\r?\n(.+?)\r?\n```\r?$/m) do