SQL procedures

This adds a new object type "procedure" that is similar to a function
but does not have a return type and is invoked by the new CALL statement
instead of SELECT or similar.  This implementation is aligned with the
SQL standard and compatible with or similar to other SQL implementations.

This commit adds new commands CALL, CREATE/ALTER/DROP PROCEDURE, as well
as ALTER/DROP ROUTINE that can refer to either a function or a
procedure (or an aggregate function, as an extension to SQL).  There is
also support for procedures in various utility commands such as COMMENT
and GRANT, as well as support in pg_dump and psql.  Support for defining
procedures is available in all the languages supplied by the core
distribution.

While this commit is mainly syntax sugar around existing functionality,
future features will rely on having procedures as a separate object
type.

Reviewed-by: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>

src/pl/plpython/sql/plpython_call.sql

@@ -0,0 +1,41 @@
+--
+-- Tests for procedures / CALL syntax
+--
+
+CREATE PROCEDURE test_proc1()
+LANGUAGE plpythonu
+AS $$
+pass
+$$;
+
+CALL test_proc1();
+
+
+-- error: can't return non-None
+CREATE PROCEDURE test_proc2()
+LANGUAGE plpythonu
+AS $$
+return 5
+$$;
+
+CALL test_proc2();
+
+
+CREATE TABLE test1 (a int);
+
+CREATE PROCEDURE test_proc3(x int)
+LANGUAGE plpythonu
+AS $$
+plpy.execute("INSERT INTO test1 VALUES (%s)" % x)
+$$;
+
+CALL test_proc3(55);
+
+SELECT * FROM test1;
+
+
+DROP PROCEDURE test_proc1;
+DROP PROCEDURE test_proc2;
+DROP PROCEDURE test_proc3;
+
+DROP TABLE test1;