Fixed: Problem with encoding in attachment (bug#10275).
Squashed commit of the following:

commit d953a1c0a29afe2e2f36d717cd983a7cbe86e52b
Author: s7design <otrs@s7designcreative.com>
Date:   Thu Mar 6 18:49:56 2014 +0100

    Fixed for all versions IE (8-11)

commit ae2e4e70f7419406abd6b7facecbe3f6b607858e
Author: s7design <otrs@s7designcreative.com>
Date:   Wed Mar 5 22:26:49 2014 +0100

    [Bug 10275] Problem with encoding in attachment

    Added code for encoding unicode filename in attachment in IE (up to version IE 10)