A document's named getter collects elements with either matching name or
id's (varies per element type) and returns them .
We implement this the following way:
* Create an iterator with elements whose `name` attribute matches
* Create an iterator with elements whose `id` attribute matches
* Concatenate both
The spec then asks us if there is more than one element in the list,
which we implement by checking whether the iterator returns `None` after
we get the first element. However, the same element can appear in both
iterators if it is a `img` element and both it's name and id attribute
match. Therefore, we need to check if there are more elements *which are
not equal to the first one*.
Testing: New web platform tests pass
---------
Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>