pgsql: Free libxml2/libxslt resources in a safer order.

Free libxml2/libxslt resources in a safer order.

Mark Simonetti reported that libxslt sometimes crashes for him, and that
swapping xslt_process's object-freeing calls around to do them in reverse
order of creation seemed to fix it.  I've not reproduced the crash, but
valgrind clearly shows a reference to already-freed memory, which is
consistent with the idea that shutdown of the xsltTransformContext is
trying to reference the already-freed stylesheet or input document.
With this patch, valgrind is no longer unhappy.

I have an inquiry in to see if this is a libxslt bug or if we're just
abusing the library; but even if it's a library bug, we'd want to adjust
our code so it doesn't fail with unpatched libraries.

Back-patch to all supported branches, because we've been doing this in
the wrong(?) order for a long time.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/c393847a1f8b35252f880853a2fd5eabd9a6d7b0

Modified Files
--------------
contrib/xml2/xslt_proc.c |   18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)