pgsql: Ensure that user created rows in extension tables get dumped if

Ensure that user created rows in extension tables get dumped if the table is explicitly requested, either with a
-t/--tableswitch of the table itself, or by -n/--schema switch of the schema containing the extension table. Patch
reviewedby Vibhor Kumar and Dimitri Fontaine. 

Backpatched to 9.1 when the extension management facility was added.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/359c8e4545a0d67465205353bd0b086aedbf5293

Modified Files
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src/bin/pg_dump/pg_dump.c |   51 +++++++++++++++++++++++++++++++++++---------
1 files changed, 40 insertions(+), 11 deletions(-)