option to disable call to xmlCleanupParser in raptor_libxml_finish

[grandinj]

So I'm doing to work to improve LibreOffice, running clang TSAN over it.

And one of the issues it flagged is actually a long standing problem, that is triggered when handling shutdown with libxml.

The problem is this - if one library calls xmlCleanupParser, then another library might crash during its shutdown code.

In this case, raptor manages to run first (sometimes) and then ICU crashes.

So it would be nice if there was an option to say "please don't call that when shutting down".

Thanks!