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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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/95a07c1ebe78444177b15cf77b80fbaa8380bb56

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