Markdown.Sanitizer removes <a href= and <img src= tags referencing relative paths

```
The part
(https?:\/\/|\/)
in Markdown.Sanitizer var img_white only allows full URLs:
http://... or https://...
or in-site URLs relative to the root
/...

As a consequence, the markdown code
"

producing the html code

is removed by Markdown.Sanitizer, because the in-site URL is relative to the
current path.

The same applies to var a_white

Solution:
Add an extra ? as follows:
(https?:\/\/|\/?)

```

Original issue reported on code.google.com by `geet...@yahoo.co.uk` on 9 Oct 2014 at 12:44

查看 Markdown.Sanitizer 的程式碼，可能位於名為 sanitizer.js 或類似名稱的檔案中。找出目前會封鎖相對路徑的 img_white 和 a_white 正規表示式模式。更新正規表示式以允許可選的前置斜線，然後建立一個包含相對圖片路徑的 Markdown 片段進行測試，並確認它沒有被移除。

由索引模型根據 Issue 內容生成。