pgsql: In pg_dump, dump SEQUENCE SET items in the data not pre-data sec

In pg_dump, dump SEQUENCE SET items in the data not pre-data section.

Represent a sequence's current value as a separate TableDataInfo dumpable
object, so that it can be dumped within the data section of the archive
rather than in pre-data. This fixes an undesirable inconsistency between
the meanings of "--data-only" and "--section=data", and also fixes dumping
of sequences that are marked as extension configuration tables, as per a
report from Marko Kreen back in July. The main cost is that we do one more
SQL query per sequence, but that's probably not very meaningful in most
databases.

Back-patch to 9.1, since it has the extension configuration issue even
though not the --section switch.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/5110a96992e508b220a7a6ab303b0501c4237b4a

Modified Files
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src/bin/pg_dump/pg_dump.c | 345 ++++++++++++++++++++++++---------------------
1 files changed, 186 insertions(+), 159 deletions(-)