pgsql: Properly enforce pg_dump -F formation options; only single letter

Log Message:
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Properly enforce pg_dump -F formation options; only single letter or
full words support, per report from Mark Stosberg.

Modified Files:
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pgsql/src/bin/pg_dump:
pg_dump.c (r1.461 -> r1.462)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dump.c.diff?r1=1.461&r2=1.462)