Index: mime_type.rb
===================================================================
--- mime_type.rb	(revision 17467)
+++ mime_type.rb	(working copy)
@@ -15,8 +15,6 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
-require 'mime/types'
-
 module Redmine
   module MimeType
 
@@ -62,15 +60,15 @@
     # returns mime type for name or nil if unknown
     def self.of(name)
       return nil unless name.present?
-      if m = name.to_s.match(/(^|\.)([^\.]+)$/)
-        extension = m[2].downcase
-        @known_types ||= Hash.new do |h, ext|
-          type = EXTENSIONS[ext]
-          type ||= MIME::Types.type_for(ext).first.to_s.presence
-          h[ext] = type
+      ext = File.extname(name)[1..-1].to_s
+      ext.downcase!
+      EXTENSIONS[ext] ||
+        MiniMime::Db::LOCK.synchronize do
+          db = MiniMime::Db.instance_variable_get(:@db)
+          db ||= MiniMime::Db.instance_variable_set(:@db, MiniMime::Db.new)
+          lookup = db.lookup_by_extension(ext)
+          lookup.content_type if lookup
         end
-        @known_types[extension]
-      end
     end
 
     # Returns the css class associated to
@@ -77,7 +75,7 @@
     # the mime type of name
     def self.css_class_of(name)
       mime = of(name)
-      mime && mime.gsub('/', '-')
+      mime && mime.tr('/', '-')
     end
 
     def self.main_mimetype_of(name)