Don't show links between Docs sites in the TOC

(e.g. if you link to /installfest/editors from the Rails course)

Author: tjgrathwell

lib/contents.rb

@@ -36,6 +36,7 @@ def subpages_for filename
     # but NOT images of the form ![alt text](image_link.jpg)
     content.scan /[^!]\[.*?\]\((.*?)\)/ do |link, _|
       next if (link =~ /^http/)
+      next if (link =~ %r(^.+/)) # cross-links to other sites, e.g. /installfest/editors
       next if (link =~ %r(^//)) # protocol-less absolute links e.g. //google.com
       links.push(link)
     end