pgsql: Update type-conversion documentation for long-ago changes.

Update type-conversion documentation for long-ago changes.

This example wasn't updated when we changed the behavior of bpcharlen()
in 8.0, nor when we changed the number of parameters taken by the bpchar()
cast function in 7.3.  Per report from lsliang.

Branch
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REL8_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1426abb516e8ddd2deca25c43b6a5326fcf8a374

Modified Files
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doc/src/sgml/typeconv.sgml |   22 ++++++++++++----------
1 files changed, 12 insertions(+), 10 deletions(-)