Fix gist_bool_ops to use gbtreekey2

Commit 57e3c5160b added a new GiST bool opclass, but it used gbtreekey4
to store the data, which left two bytes undefined, as reported by skink,
our valgrind animal. There was a bit more confusion, because the opclass
also used gbtreekey8 in the definition.

Fix by defining a new gbtreekey2 struct, and using it in all the places.

Discussion: https://postgr.es/m/CAE2gYzyDKJBZngssR84VGZEN=Ux=V9FV23QfPgo+7-yYnKKg4g@mail.gmail.com

contrib/btree_gist/btree_bool.c

@@ -72,7 +72,7 @@ static const gbtree_ninfo tinfo =
 {
 	gbt_t_bool,
 	sizeof(bool),
-	4,							/* sizeof(gbtreekey4) */
+	2,							/* sizeof(gbtreekey2) */
 	gbt_boolgt,
 	gbt_boolge,
 	gbt_booleq,

contrib/btree_gist/btree_gist--1.6--1.7.sql

@@ -4,6 +4,21 @@
 \echo Use "ALTER EXTENSION btree_gist UPDATE TO '1.7'" to load this file. \quit
 
 -- This upgrade scripts add support for bool.
+CREATE FUNCTION gbtreekey2_in(cstring)
+RETURNS gbtreekey2
+AS 'MODULE_PATHNAME', 'gbtreekey_in'
+LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
+CREATE FUNCTION gbtreekey2_out(gbtreekey2)
+RETURNS cstring
+AS 'MODULE_PATHNAME', 'gbtreekey_out'
+LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
+CREATE TYPE gbtreekey2 (
+	INTERNALLENGTH = 2,
+	INPUT  = gbtreekey2_in,
+	OUTPUT = gbtreekey2_out
+);
 
 -- Define the GiST support methods
 CREATE FUNCTION gbt_bool_consistent(internal,bool,int2,oid,internal)
@@ -32,11 +47,11 @@ AS 'MODULE_PATHNAME'
 LANGUAGE C IMMUTABLE STRICT;
 
 CREATE FUNCTION gbt_bool_union(internal, internal)
-RETURNS gbtreekey8
+RETURNS gbtreekey2
 AS 'MODULE_PATHNAME'
 LANGUAGE C IMMUTABLE STRICT;
 
-CREATE FUNCTION gbt_bool_same(gbtreekey8, gbtreekey8, internal)
+CREATE FUNCTION gbt_bool_same(gbtreekey2, gbtreekey2, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
 LANGUAGE C IMMUTABLE STRICT;
@@ -57,6 +72,6 @@ AS
 	FUNCTION	4	gbt_decompress (internal),
 	FUNCTION	5	gbt_bool_penalty (internal, internal, internal),
 	FUNCTION	6	gbt_bool_picksplit (internal, internal),
-	FUNCTION	7	gbt_bool_same (gbtreekey8, gbtreekey8, internal),
+	FUNCTION	7	gbt_bool_same (gbtreekey2, gbtreekey2, internal),
 	FUNCTION	9   gbt_bool_fetch (internal),
-	STORAGE		gbtreekey8;
+	STORAGE		gbtreekey2;