pgsql: Ignore XML declaration in xpath_internal(), for UTF8 databases.

Ignore XML declaration in xpath_internal(), for UTF8 databases.

When a value contained an XML declaration naming some other encoding,
this function interpreted UTF8 bytes as the named encoding, yielding
mojibake. xml_parse() already has similar logic. This would be
necessary but not sufficient for non-UTF8 databases, so preserve
behavior there until the xpath facility can support such databases
comprehensively. Back-patch to 9.3 (all supported versions).

Pavel Stehule and Noah Misch

Discussion: https://postgr.es/m/CAFj8pRC-dM=tT=QkGi+Achkm+gwPmjyOayGuUfXVumCxkDgYWg@mail.gmail.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/30a5e940ac9a96c5fee449223528a1b5555502ed

Modified Files
--------------
src/backend/utils/adt/xml.c | 14 +++++++++++++-
src/test/regress/expected/xml.out | 31 +++++++++++++++++++++++++++++++
src/test/regress/expected/xml_1.out | 35 +++++++++++++++++++++++++++++++++++
src/test/regress/expected/xml_2.out | 31 +++++++++++++++++++++++++++++++
src/test/regress/sql/xml.sql | 32 ++++++++++++++++++++++++++++++++
5 files changed, 142 insertions(+), 1 deletion(-)