plpython security and error handling fixes, from

Kevin Jacobs and Brad McLean.

src/pl/plpython/plpython_error.sql

@@ -7,3 +7,11 @@ SELECT invalid_type_uncaught('rick');
 SELECT invalid_type_caught('rick');
 SELECT invalid_type_reraised('rick');
 SELECT valid_type('rick');
+
+-- Security sandbox tests
+SELECT read_file('/etc/passwd');
+SELECT write_file('/tmp/plpython','This is very bad');
+SELECT getpid();
+SELECT uname();
+SELECT sys_exit();
+SELECT sys_argv();