Use less to build all CSS files

CSS file names are now updated when visitor's browser must reload them
Allow files with .css extension to skip less compilation (IE6 invalid CSS syntax)

_layouts/base.html

@@ -20,9 +20,9 @@ menu:
 <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
 <title>{% capture title %}{% translate title %}{% endcapture %}{% if title != '' %}{{ title }}{% else %}{{ page.title }}{% endif %}</title>
 {% lesscss main.less %}
-<!--[if lt IE 8]><link rel="stylesheet" type="text/css" href="/css/ie.css" /><script type="text/javascript" src="/js/ie.js"></script><![endif]-->
-{% if page.lang == 'ar' or page.lang == 'fa' %}<link rel="stylesheet" type="text/css" href="/css/rtl.css">{% endif %}
-{% if page.lang == 'pl' or page.lang == 'ru' or page.lang == 'zh_CN' or page.lang == 'zh_TW' %}<link rel="stylesheet" type="text/css" href="/css/sans.css">{% endif %}
+<!--[if lt IE 8]>{% lesscss ie.css %}<script type="text/javascript" src="/js/ie.js"></script><![endif]-->
+{% if page.lang == 'ar' or page.lang == 'fa' %}{% lesscss rtl.less %}{% endif %}
+{% if page.lang == 'pl' or page.lang == 'ru' or page.lang == 'zh_CN' or page.lang == 'zh_TW' %}{% lesscss sans.less %}{% endif %}
 <script type="text/javascript" src="/js/main.js"></script>
 <link rel="shortcut icon" href="/favicon.png">
 <link rel="apple-touch-icon-precomposed" href="/img/logo_ios.png"/>

_plugins/less.rb

@@ -30,10 +30,15 @@ module Jekyll
       Dir.chdir(less_dir) do
         choices = Dir['**/*'].reject { |x| File.symlink?(x) }
         if choices.include?(@file)
+
+          if /\.css$/.match(@file)
+            f = file = File.new(@file, "r")
+          else
             source = File.read(@file)
             f = IO.popen("lessc -", "w+")
             f.write(source)
             f.close_write()
+          end
 
           css = f.readlines().join()