URI of DocBook XSL doesn't work on Trisquel 10.0.1, which is our build-test docker image

[strk]

The URI we're using right now (DOCBOOK_XSLBASE) is ​http://cdn.docbook.org/release/xsl/current but some systems are not able to resolve it correctly with their xml catalog.

On Trisquel 10.0.1 which is our current postgis-docker.osgeo.org:postgis/build-test docker image those URIs don't work:

# xmlcatalog '' http://cdn.docbook.org/release/xsl/current
No entry for SYSTEM http://cdn.docbook.org/release/xsl/current
No entry for URI http://cdn.docbook.org/release/xsl/current

But older (legacy) uri work:

# xmlcatalog '' http://docbook.sourceforge.net/release/xsl-ns/current/html/docbook.xsl
file:///usr/share/xml/docbook/stylesheet/docbook-xsl-ns/html/docbook.xsl

This ticket is use the legacy URL or eventually add a configure-time check to see which URI works or give up if none work. Doing this at configure time would be similar to what we were doing before commit [b6583e98323ffe1a8438b51f3a9c70205fdbcf6b/git] that is allow some kind of configure-time switch to find those xsl. See also ticket #5537 and #5538

[Sandro Santilli <strk@…>]

In 2a366e9/git:

Use the legacy URI for docbook.xsl

References #5539

[strk]

OOps, debbie would fail the legacy url:

debbie:~# xmlcatalog "" http://docbook.sourceforge.net/release/xsl-ns/html/docbook.xsl
No entry for SYSTEM http://docbook.sourceforge.net/release/xsl-ns/html/docbook.xsl
No entry for URI http://docbook.sourceforge.net/release/xsl-ns/html/docbook.xsl

See also ​https://github.com/docbook/xslt10-stylesheets/pull/259

[strk]

Sorry I meant see ​https://github.com/docbook/xslt10-stylesheets/issues/201

[Sandro Santilli <strk@…>]

In 119b6e4/git:

Go back to find docbook XSL at configure time

This reverts commit b6583e98323ffe1a8438b51f3a9c70205fdbcf6b
bringing —with-xsldir support back.

Closes #5538 #5539

References #5537