Use Gitlab Markdown for Markdown files and Gollum to render the rest.

This commit enables the usage of the Gitlab Markdown post processing
on all Markdown formatted files. For file types that do not contain
Markdown, it defaults to the Gollum native renderer to process the
content.

app/helpers/gitlab_markdown_helper.rb

@@ -49,4 +49,12 @@ module GitlabMarkdownHelper
 
     @markdown.render(text).html_safe
   end
+
+  def render_wiki_content(wiki_page)
+    if wiki_page.format == :markdown
+      markdown(wiki_page.content)
+    else
+      wiki_page.formatted_content.html_safe
+    end
+  end
 end

app/views/wikis/show.html.haml

@@ -10,7 +10,7 @@
 .file_holder
   .file_content.wiki
     = preserve do
-      = @wiki.formatted_content.html_safe
+      = render_wiki_content(@wiki)
 
 - commit = CommitDecorator.new(@wiki.version)
 %p.time Last edited by #{commit.author_link(avatar: true, size: 16)} #{time_ago_in_words @wiki.created_at} ago