pgsql: Add a \sf (show function) command to psql, for those times when

Log Message:
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Add a \sf (show function) command to psql, for those times when you need to
look at a function but don't wish to fire up an editor.

Pavel Stehule, reviewed by Jan Urbanski

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
psql-ref.sgml (r1.248 -> r1.249)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml?r1=1.248&r2=1.249)
pgsql/src/bin/psql:
command.c (r1.226 -> r1.227)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c?r1=1.226&r2=1.227)
help.c (r1.162 -> r1.163)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/help.c?r1=1.162&r2=1.163)
tab-complete.c (r1.201 -> r1.202)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c?r1=1.201&r2=1.202)