IE7 and iframeTarget fixes

[emasab]

Hi malsup, here is the pull request that you asked me. Sorry for the delay, but I was kind of busy.

[kevindb]

Is this PR still necessary?

Possibly related to #358 custom iframeTarget doesn't attach load listener
Possibly resolved by d0e782f

[emasab]

for the ownerDocument thing, The problem was that
http://stackoverflow.com/questions/2284356/cant-appendchild-to-a-node-created-from-another-frame
maybe it's present in IE10 too, because here states
https://msdn.microsoft.com/en-us/library/gg592979(v=vs.85).aspx

The node is owned by a different document and cannot be used. Starting with Internet Explorer 10, the error-code string WrongDocumentError is returned instead.

It usually happens when using jQuery from the opener window and the form is in the opened window.

The move of
if (io.attachEvent)
is necessary for the custom iframeTarget

[kevindb]

Whew! This gets messy with a four year old PR. It looks like d0e782f (8 months after your PR) took care of moving if (io.attachEvent).

Would you please update your PR (or create a new one, if that's easier) from current master for your form.ownerDocument and $form.closest('body') changes?

[emasab]

here is the new PR

#518