Readme rendering fix

王权利请求将github/fork/dfyx/readme_rendering_fix合并到master

Created by: dfyx

Quick fix for #1676. A more elegant solution would be to share code between app/views/tree/_readme.html.haml and app/views/blob/_text.html.haml but I'm not that good with HAML and it works for now.

合并请求报告