Stream append/prepend can produce duplicates if the template element is a form

[ethancrawford]

Hi! So, I noticed that if you try to append or prepend a form which contains a child form control with the name 'id', (such as in this minimal-ish example):

<form id="myform">
  <input name="id">
</form>

...then the 'old' form is not removed when the new one is appended/prepended.
(Since myform.id will then refer to the named child control, not the form's id attribute, and the id match created previously to remove duplicates fails).

[seanpdoyle]

Thank you for opening this issue.

I've opened #1037 to deal with a similar collision with regard to the [action] attribute.