CSS images do not have "url()" when using --self-contained option

[prigio]

When using the --self-contained option to convert markdown->html, data-uri images within CSS miss the enclosing "url()" and are therefore not displayed.

Pandoc version: 1.15.1 on OsX.

Sample files:

• index.md

  <link rel="stylesheet" href="test.css" type="text/css" />
  
  This is some content. 
  
  The body element has a background image.
  

• test.css

  body {
  background: white url('http://www.git-scm.com/images/[email protected]') no-repeat left 80px;
  }
  

Command lines used to produce the comparison files:

pandoc -f markdown -t html --standalone -o index.html index.md
pandoc -f markdown -t html --standalone --self-contained -o index_sc.html index.md