[xml] libxslt test suite broken by recent libxml2 commit

[Nick Wellnhofer <wellnhofer aevum de>]

The following commit to libxml2 causes the libxslt test suite to break:

https://git.gnome.org/browse/libxml2/commit/?id=a16eb968075a82ec33b2c1e77db8909a35b44620

Some tests like general/bug-110 fail because of a new warning message like “validity error : ID id0 already 
defined”. A simple way to reproduce is:

$ xmllint --noent --noout tests/docs/bug-110.xml 
tests/docs/bug-110.xml:1: element elem: validity error : ID id0 already defined

This is somehow related to the --noent option and it looks like a bug in libxml2 to me. First of all, I 
wonder why I get the warning without the --valid option. Second, I can’t see why the id attribute would be 
already defined.

Nick