Further eww dom.el cleanups

* net/eww.el (eww-tag-title): Use `dom-text'.

* dom.el (dom-by-tag): Use `equal' for comparisons so that tags
can be strings.
(dom-elements): Protect against non-text nodes.
(dom-non-text-children): New function.
* gnutls.c (Fgnutls_boot): Send the server name over

Fixes: debbugs:18208

* gnutls.c (Fgnutls_boot): Send the server name over (bug#18208).