Update gratuitous use of MD5 in documentation

It seems some people are bothered by the outdated MD5 appearing in
example code.  So replace it with more modern alternatives or by
a different example function.
Reported-by: Jon Wolski <jonwolski@gmail.com>

doc/src/sgml/citext.sgml

@@ -80,11 +80,11 @@ CREATE TABLE users (
     pass TEXT   NOT NULL
 );
 
-INSERT INTO users VALUES ( 'larry',  md5(random()::text) );
-INSERT INTO users VALUES ( 'Tom',    md5(random()::text) );
-INSERT INTO users VALUES ( 'Damian', md5(random()::text) );
-INSERT INTO users VALUES ( 'NEAL',   md5(random()::text) );
-INSERT INTO users VALUES ( 'Bjørn',  md5(random()::text) );
+INSERT INTO users VALUES ( 'larry',  sha256(random()::text::bytea) );
+INSERT INTO users VALUES ( 'Tom',    sha256(random()::text::bytea) );
+INSERT INTO users VALUES ( 'Damian', sha256(random()::text::bytea) );
+INSERT INTO users VALUES ( 'NEAL',   sha256(random()::text::bytea) );
+INSERT INTO users VALUES ( 'Bjørn',  sha256(random()::text::bytea) );
 
 SELECT * FROM users WHERE nick = 'Larry';
 </programlisting>

doc/src/sgml/sepgsql.sgml

@@ -370,7 +370,7 @@ $ sudo semodule -r sepgsql-regtest
    <para>
    For example, consider:
 <synopsis>
-UPDATE t1 SET x = 2, y = md5sum(y) WHERE z = 100;
+UPDATE t1 SET x = 2, y = func1(y) WHERE z = 100;
 </synopsis>
 
     Here, <literal>db_column:update</literal> will be checked for