[xml] Adding new slot in parser.h::_xmlParserCtxt

[Lilith <lilith zenteq am>]

Hello,

I use libxml2, libxslt, and libxml2-python. In some tasks I need to  
redefine the default entity loader. My application runs in multithreaded  
mode, and each thread must have a different loader . Also imported and  
included stylesheets must be loaded with the same loader as their parent  
stylesheet. To implement this, I did the following:
1) added new `loaderId' slot in libxml2::include/libxml/tree.h:_xmlDoc  
structure;
2) added new `loaderId' slot in libxml2::include/libxml/parser.h:  
_xmlParserCtxt;
3) modified function `xsltDocDefaultLoaderFunc' changing the type of the  
fourth argument to `xsltStylesheetPtr ctxt' and added the following:
              pctxt = xmlNewParserCtxt();
        /* hacked */
        if (ctxt) {
                par = ctxt->parent;
                loaderId = ctxt->doc->loaderId;
                pctxt->loaderId = doc->loaderId = (xsltStylesheet *)ctxt->doc->loaderId;
        }
to `xsltDocDefaultLoaderFunc' (and modified every call of this function to  
pass the right argument);
4) added accessors for `loaderId' to the python wrappers in `parserCtxt'  
and `xmlDoc' classes;

After that, I get the `segmentation fault' somewhere (I really don't know  
where, because it changes depending on where I place the `loaderId' slot  
in '_xmlParserCtxt').
How can I implement what I needed and what is happening when I add a new  
slot in _xmlParserCtxt? There was a similar trouble when I added  
`loaderId' as the first slot to _xmlDoc, and I fixed it by moving it to  
the bottom of the structure. The problem was that `xmlElementType' must be  
the second slot. But there are no similar restrictions in `_xmlParserCtxt'.

Lilith
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