pgsql: Experiment with using EXPLAIN COSTS OFF in regression tests.

Log Message:
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Experiment with using EXPLAIN COSTS OFF in regression tests.

This is a simple test to see whether COSTS OFF will help much with getting
EXPLAIN output that's sufficiently platform-independent for use in the
regression tests. The planner does have some freedom of choice in these
examples (plain via bitmap indexscan), so I'm not sure what will happen.

Modified Files:
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pgsql/src/test/regress/expected:
create_index.out (r1.29 -> r1.30)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_index.out?r1=1.29&r2=1.30)
pgsql/src/test/regress/sql:
create_index.sql (r1.25 -> r1.26)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/create_index.sql?r1=1.25&r2=1.26)