Makes User.current thread safe (#12097).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@10911 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/user.rb

@@ -601,11 +601,11 @@ class User < Principal
   end
 
   def self.current=(user)
-    @current_user = user
+    Thread.current[:current_user] = user
   end
 
   def self.current
-    @current_user ||= User.anonymous
+    Thread.current[:current_user] ||= User.anonymous
   end
 
   # Returns the anonymous user.  If the anonymous user does not exist, it is created.  There can be only