pgsql: Fix SortTocFromFile() to cope with lines that are too long for i

Fix SortTocFromFile() to cope with lines that are too long for its buffer.

The original coding supposed that a dump TOC file could never contain lines
longer than 1K.  The folly of that was exposed by a recent report from
Per-Olov Esgard.  We only really need to see the first dozen or two bytes
of each line, since we're just trying to read off the numeric ID at the
start of the line; so there's no need for a particularly huge buffer.
What there is a need for is logic to not process continuation bufferloads.

Back-patch to all supported branches, since it's always been like this.

Branch
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REL8_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/9a9c7c2eb10b8df67c5652a6678a172b83a262eb

Modified Files
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src/bin/pg_dump/pg_backup_archiver.c |   29 ++++++++++++++++++++++++-----
1 files changed, 24 insertions(+), 5 deletions(-)