bug#13025: 24.2.90; sgml-electric-tag-pair-mode broken

[Leo]

Turn on sgml-electric-tag-pair-mode in html mode and try to modify a
nonvoid tag such as 'title' or 'body'.

If you delete the opening tag (the thing inside <>) using kill-word or
backward-kill-word, nothing happens to the closing tag.

If you delete the tag one char at a time, the closing tag stops at the
last char, so you end up with a pair such as <></y>, now if you
re-insert a tag that doesn't start with 'y', nothing happens to the
closing tag.

The above behaviour is consistent since the feature was added, i.e. it
happens in 23, 24.2 and 24.2.90.

Leo