applied fix for accessor functions of a stylesheet returning pointers to

* python/libxslt-python-api.xml: applied fix for accessor functions
  of a stylesheet returning pointers to immutable strings, patch
  from #320540
* xsltproc/xsltproc.c: fix the xinclude on stylehseet problem
  by adding a new parameter to xsltproc names --xincludestyle
Daniel