Second try at stabilizing query plans in rowsecurity regression test.

This reverts commit 5cdf25e168,
which was almost immediately proven insufficient by the buildfarm.

On second thought, the tables involved are not large enough that
autovacuum or autoanalyze would notice them; what seems far more
likely to be the culprit is the database-wide "vacuum analyze"
in the concurrent gist test.  That thing has given us one headache
too many, so get rid of it in favor of targeted vacuuming of that
test's own tables only.

src/test/regress/sql/gist.sql

@@ -22,7 +22,7 @@ delete from gist_point_tbl where id % 2 = 1;
 -- would exercise it)
 delete from gist_point_tbl where id < 10000;
 
-vacuum gist_point_tbl;
+vacuum analyze gist_point_tbl;
 
 
 --
@@ -37,7 +37,7 @@ select box(point(0.05*i, 0.05*i), point(0.05*i, 0.05*i)),
        circle(point(0.05*i, 0.05*i), 1.0)
 from generate_series(0,10000) as i;
 
-vacuum analyze;
+vacuum analyze gist_tbl;
 
 set enable_seqscan=off;
 set enable_bitmapscan=off;