[xml] Freeing the schema document in schematron

[Stefan Behnel <stefan_ml behnel de>]

Hi,

I keep running into segfaults when freeing the document I pass into
xmlSchematronNewDocParserCtxt(). It looks like the "preserve" flag in the
xmlSchematron struct is not set correctly in xmlSchematronParse(). There is a
local variable that is set instead, but never stored in the struct.

Stefan