pgsql: Make pg_regress use CREATE OR REPLACE LANGUAGE, so that

Log Message:
-----------
Make pg_regress use CREATE OR REPLACE LANGUAGE, so that --load-language
will work whether or not the specified language is preinstalled.  This
responds to some complaints about having to change test scripts because
plpgsql is preinstalled as of 9.0.

Modified Files:
--------------
    pgsql/src/test/regress:
        pg_regress.c (r1.69 -> r1.70)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.c?r1=1.69&r2=1.70)