Merged r13101 from trunk to 2.5-stable (#16711)

fix non-ascii attachment file name get corrupted in IE11.

Contributed by Go MAEDA.

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13102 e93f8b46-1217-0410-a6f0-8f06a7374b81