pgsql: Improve testlibpq3.c's example of PQexecParams() usage to include

Log Message:
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Improve testlibpq3.c's example of PQexecParams() usage to include sending
a parameter in binary format.  Also, add a TIP explaining how to use casts
in the query text to avoid needing to specify parameter types by OID.
Also fix bogus spacing --- apparently somebody expanded the tabs in the
example programs to 8 spaces instead of 4 when transposing them into SGML.

Modified Files:
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    pgsql/doc/src/sgml:
        libpq.sgml (r1.195 -> r1.196)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.195&r2=1.196)
    pgsql/src/test/examples:
        testlibpq3.c (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/examples/testlibpq3.c.diff?r1=1.12&r2=1.13)