This patch updates the DDL for contrib/pgcrypto to create all

functions as STRICT, and all functions except gen_salt() as IMMUTABLE.
gen_salt() is VOLATILE.

Although the functions are now STRICT, I left their PG_ARGISNULL()
checks in place as a protective measure for users who install the
new code but use old (non-STRICT) catalog entries (e.g., restored
from a dump).  Per recent discussion in pgsql-hackers.

Patch from Michael Fuhr.

contrib/pgcrypto/pgcrypto.sql.in

@@ -4,71 +4,71 @@ SET search_path = public;
 CREATE OR REPLACE FUNCTION digest(text, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_digest'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION digest(bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_digest'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION digest_exists(text)
 RETURNS bool
 AS 'MODULE_PATHNAME', 'pg_digest_exists'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION hmac(text, text, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_hmac'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION hmac(bytea, bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_hmac'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION hmac_exists(text)
 RETURNS bool
 AS 'MODULE_PATHNAME', 'pg_hmac_exists'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION crypt(text, text)
 RETURNS text
 AS 'MODULE_PATHNAME', 'pg_crypt'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION gen_salt(text)
 RETURNS text
 AS 'MODULE_PATHNAME', 'pg_gen_salt'
-LANGUAGE 'C';
+LANGUAGE 'C' VOLATILE STRICT;
 
 CREATE OR REPLACE FUNCTION gen_salt(text, int4)
 RETURNS text
 AS 'MODULE_PATHNAME', 'pg_gen_salt_rounds'
-LANGUAGE 'C';
+LANGUAGE 'C' VOLATILE STRICT;
 
 CREATE OR REPLACE FUNCTION encrypt(bytea, bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_encrypt'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION decrypt(bytea, bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_decrypt'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION encrypt_iv(bytea, bytea, bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_encrypt_iv'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION decrypt_iv(bytea, bytea, bytea, text)
 RETURNS bytea
 AS 'MODULE_PATHNAME', 'pg_decrypt_iv'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;
 
 CREATE OR REPLACE FUNCTION cipher_exists(text)
 RETURNS bool
 AS 'MODULE_PATHNAME', 'pg_cipher_exists'
-LANGUAGE 'C';
+LANGUAGE 'C' IMMUTABLE STRICT;