Patch for disable_with option to submit_tag (broken on IE)

The disable_with option to submit_tag is broken on IE (all versions).
The current implementation changes the type attribute of an existing
element in javascript, something that is not supported in IE.

I made a patch about a month ago (https://rails.lighthouseapp.com/
projects/8994/tickets/1955-disable_with-option-to-submit_tag-doesnt-
work-with-ie#ticket-1955-2). It is still valid for 2-3-stable and
master.

It would be great if someone could verify this patch.

Thanks,

Han