修复当课程描述中有特殊标签是，课程列表描述显示有误的BUG

app/models/course.rb

@@ -92,10 +92,21 @@ class Course < ActiveRecord::Base
 
   # 课程的短描述信息
   def short_description(length = 255)
-    description.gsub(/<\/?.*?>/,"").strip if description
+    description.gsub(/<\/?.*?>/,"").html_safe if description
     #description.gsub(/^(.{#{length}}[^\n\r]*).*$/m, '\1...').strip if description
   end
 
+  def strip_html(html)
+    return html if html.empty? || !html.include?('<')
+    output = ""
+    tokenizer = HTML::Tokenizer.new(html)
+    while token = tokenizer.next
+      node = HTML::Node.parse(nil, 0, 0, token, false)
+      output += token unless (node.kind_of? HTML::Tag) or (token =~ /^<!/)
+    end
+    return output
+  end
+
   def extra_frozen?
     errors[:extra].blank? && !(new_record? || extra.blank?)
   end