pgsql: Fix namespace handling in xpath function

Fix namespace handling in xpath function

Previously, the xml value resulting from an xpath query would not have
namespace declarations if the namespace declarations were attached to
an ancestor element in the input xml value.  That means the output value
was not correct XML.  Fix that by running the result value through
xmlCopyNode(), which produces the correct namespace declarations.

Author: Ali Akbar <the.apaan@gmail.com>

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/e32cb8d0e02f8f3fa2c66d80b5cf0ad762c79c9d

Modified Files
--------------
src/backend/utils/adt/xml.c         |   34 ++++++++++++++++++++++++++--------
src/test/regress/expected/xml.out   |   15 +++++++++++++++
src/test/regress/expected/xml_1.out |   12 ++++++++++++
src/test/regress/sql/xml.sql        |    2 ++
4 files changed, 55 insertions(+), 8 deletions(-)