Route /filename/[commit-sha] will display specific revision of a file. Resolves #892.

lib/gollum/app.rb

@@ -402,6 +402,8 @@ module Precious
         @content = page.formatted_data
         @version = version
         mustache :page
+      elsif file = wikip.wiki.file("#{file_path}", version, true)
+        show_file(file)
       else
         halt 404
       end
@@ -472,18 +474,23 @@ module Precious
 
         mustache :page
       elsif file = wiki.file(fullpath, wiki.ref, true)
-        if file.on_disk?
-          send_file file.on_disk_path, :disposition => 'inline'
-        else
-          content_type file.mime_type
-          file.raw_data
-        end
+        show_file(file)
       else
         page_path = [path, name].compact.join('/')
         redirect to("/create/#{clean_url(encodeURIComponent(page_path))}")
       end
     end
 
+    def show_file(file)
+      return unless file
+      if file.on_disk?
+        send_file file.on_disk_path, :disposition => 'inline'
+      else
+        content_type file.mime_type
+        file.raw_data
+      end
+    end
+
     def update_wiki_page(wiki, page, content, commit, name = nil, format = nil)
       return if !page ||
           ((!content || page.raw_data == content) && page.format == format)