Make CREATE TYPE print warnings if a datatype's I/O functions are volatile.

This is a followup to commit 43ac12c6e6,
which added regression tests checking that I/O functions of built-in
types are not marked volatile.  Complaining in CREATE TYPE should push
developers of add-on types to fix any misdeclared functions in their
types.  It's just a warning not an error, to avoid creating upgrade
problems for what might be just cosmetic mis-markings.

Aside from adding the warning code, fix a number of types that were
sloppily created in the regression tests.

src/test/regress/expected/create_cast.out

@@ -6,12 +6,12 @@ CREATE TYPE casttesttype;
 CREATE FUNCTION casttesttype_in(cstring)
    RETURNS casttesttype
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type casttesttype is only a shell
 CREATE FUNCTION casttesttype_out(casttesttype)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type casttesttype is only a shell
 CREATE TYPE casttesttype (
    internallength = variable,

src/test/regress/expected/create_type.out

@@ -41,22 +41,22 @@ CREATE TYPE text_w_default;
 CREATE FUNCTION int42_in(cstring)
    RETURNS int42
    AS 'int4in'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type int42 is only a shell
 CREATE FUNCTION int42_out(int42)
    RETURNS cstring
    AS 'int4out'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type int42 is only a shell
 CREATE FUNCTION text_w_default_in(cstring)
    RETURNS text_w_default
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type text_w_default is only a shell
 CREATE FUNCTION text_w_default_out(text_w_default)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type text_w_default is only a shell
 CREATE TYPE int42 (
    internallength = 4,

src/test/regress/input/create_function_1.source

@@ -5,22 +5,22 @@
 CREATE FUNCTION widget_in(cstring)
    RETURNS widget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION widget_out(widget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION int44in(cstring)
    RETURNS city_budget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION int44out(city_budget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION check_primary_key ()
 	RETURNS trigger

src/test/regress/output/create_function_1.source

@@ -4,24 +4,24 @@
 CREATE FUNCTION widget_in(cstring)
    RETURNS widget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  type "widget" is not yet defined
 DETAIL:  Creating a shell type definition.
 CREATE FUNCTION widget_out(widget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  argument type widget is only a shell
 CREATE FUNCTION int44in(cstring)
    RETURNS city_budget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  type "city_budget" is not yet defined
 DETAIL:  Creating a shell type definition.
 CREATE FUNCTION int44out(city_budget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  argument type city_budget is only a shell
 CREATE FUNCTION check_primary_key ()
 	RETURNS trigger

src/test/regress/sql/create_cast.sql

@@ -8,11 +8,11 @@ CREATE TYPE casttesttype;
 CREATE FUNCTION casttesttype_in(cstring)
    RETURNS casttesttype
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION casttesttype_out(casttesttype)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 
 CREATE TYPE casttesttype (
    internallength = variable,

src/test/regress/sql/create_type.sql

@@ -44,19 +44,19 @@ CREATE TYPE text_w_default;
 CREATE FUNCTION int42_in(cstring)
    RETURNS int42
    AS 'int4in'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION int42_out(int42)
    RETURNS cstring
    AS 'int4out'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION text_w_default_in(cstring)
    RETURNS text_w_default
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION text_w_default_out(text_w_default)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 
 CREATE TYPE int42 (
    internallength = 4,