Merged r13346 from trunk to 2.4-stable (#17581, #13932)

fix Drag & Drop does not work with Safari 5.1.

Contributed by fred bregar.

git-svn-id: http://svn.redmine.org/redmine/branches/2.4-stable@13349 e93f8b46-1217-0410-a6f0-8f06a7374b81