Support functions for index opclasses should be immutable.

Found by running opr_sanity on contrib modules.

contrib/hstore/hstore.sql.in

@@ -186,37 +186,37 @@ CREATE TYPE ghstore (
 CREATE FUNCTION ghstore_compress(internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION ghstore_decompress(internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION ghstore_penalty(internal,internal,internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT;
+LANGUAGE C IMMUTABLE STRICT;
 
 CREATE FUNCTION ghstore_picksplit(internal, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION ghstore_union(internal, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION ghstore_same(internal, internal, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION ghstore_consistent(internal,internal,int4)
 RETURNS bool
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 -- register the opclass for indexing (not as default)
 CREATE OPERATOR CLASS gist_hstore_ops
@@ -241,23 +241,23 @@ AS
 CREATE FUNCTION gin_extract_hstore(internal, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION gin_extract_hstore_query(internal, internal, int2)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE FUNCTION gin_consistent_hstore(internal, int2, internal)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C;
+LANGUAGE C IMMUTABLE;
 
 CREATE OPERATOR CLASS gin_hstore_ops
 DEFAULT FOR TYPE hstore USING gin
 AS
 	OPERATOR        7       @> RECHECK,
-    OPERATOR        9       ?(hstore,text),
+	OPERATOR        9       ?(hstore,text),
 	FUNCTION        1       bttextcmp(text,text),
 	FUNCTION        2       gin_extract_hstore(internal, internal),
 	FUNCTION        3       gin_extract_hstore_query(internal, internal, int2),