pgsql: Clean up data conversion short-lived memory context.

Clean up data conversion short-lived memory context.

dblink uses a short-lived data conversion memory context. However it
was not deleted when no longer needed, leading to a noticeable memory
leak under some circumstances. Plug the hole, along with minor
refactoring. Backpatch to 9.2 where the leak was introduced.

Report and initial patch by MauMau. Reviewed/modified slightly by
Tom Lane and me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/1dde5782e34a1c5ef2ce9d97cf18007fed5fde92

Modified Files
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contrib/dblink/dblink.c |   22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)