Add test cases for indexam operations not currently covered.

That includes VACUUM on GIN, GiST and SP-GiST indexes, and B-tree indexes
large enough to cause page deletions in B-tree. Plus some other special
cases.

After this patch, the regression tests generate all different WAL record
types. Not all branches within the redo functions are covered, but it's a
step forward.

src/test/regress/sql/gist.sql

@@ -0,0 +1,25 @@
+--
+-- Test GiST indexes.
+--
+-- There are other tests to test different GiST opclasses. This is for
+-- testing GiST code itself. Vacuuming in particular.
+
+create table gist_point_tbl(id int4, p point);
+create index gist_pointidx on gist_point_tbl using gist(p);
+
+-- Insert enough data to create a tree that's a couple of levels deep.
+insert into gist_point_tbl (id, p)
+select g,        point(g*10, g*10) from generate_series(1, 10000) g;
+
+insert into gist_point_tbl (id, p)
+select g+100000, point(g*10+1, g*10+1) from generate_series(1, 10000) g;
+
+-- To test vacuum, delete some entries from all over the index.
+delete from gist_point_tbl where id % 2 = 1;
+
+-- And also delete some concentration of values. (GiST doesn't currently
+-- attempt to delete pages even when they become empty, but if it did, this
+-- would exercise it)
+delete from gist_point_tbl where id < 10000;
+
+vacuum gist_point_tbl;