pgsql: Adjust psql's new \ef command to present an empty CREATE FUNCTION

Log Message:
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Adjust psql's new \ef command to present an empty CREATE FUNCTION template
for editing if no function name is specified.  This seems a much cleaner way
to offer that functionality than the original patch had.  In passing,
de-clutter the error displays that are given for a bogus function-name
argument, and standardize on "$function$" as the default delimiter for the
function body.  (The original coding would use the shortest possible
dollar-quote delimiter, which seems to create unnecessarily high risk of
later conflicts with the user-modified function body.)

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        psql-ref.sgml (r1.210 -> r1.211)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml?r1=1.210&r2=1.211)
    pgsql/src/backend/utils/adt:
        ruleutils.c (r1.283 -> r1.284)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ruleutils.c?r1=1.283&r2=1.284)
    pgsql/src/bin/psql:
        command.c (r1.194 -> r1.195)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c?r1=1.194&r2=1.195)