When cross-references in the original paragraph and the translated
paragraph do not match, a warning is emitted.  It is useful, because
it allows to catch mistakes, but it can also be an annoyance since
sometimes it is expected that the cross-references will not match.
For example, a reference that is repeated in the original text may
need to be factored out for good style in the target language.
Another example: if the translator needs to translate a universally
understood term in the source language into a term that not everyone
knows is the translation of this original term, adding a reference to
the glossary can be warranted.  This allows the translated message to
start with '#noqa' in order to disable the warning.

This is done by moving the sorting from the glossary directive to a
transform operating after the i18n transform.

Closes #9827

Also change any docutils.sourceforge.net link to io
top level domain.

Trailing whitespace do not have impact on the result, they are just
unused bytes. Most text editors are configured to strip trailing
whitespaces. Remove them all in one go.

Update a handful of files to use the UNIX line ending.

To allow to give (or not to give) an explicit title to the
pending_xref nodes on translation, this skips to override the
attribute on merge original and translated documents.

Make alt text for image translatable by default without settings of
gettext_additional_targets.