BUG #2150: PL/Python function delcared STABLE gets run repeatedly

The following bug has been logged online:

Bug reference:      2150
Logged by:          Aaron Swartz
Email address:      me@aaronsw.com
PostgreSQL version: 8.1.1
Operating system:   Mac OS X
Description:        PL/Python function delcared STABLE gets run repeatedly
Details:

We have the PL/Python function get_foo(n) that returns an array. If this
function is declared IMMUTABLE, then:

SELECT * FROM tablenamehere WHERE id = any(get_foo(21));

returns quickly. If the function is declared STABLE, however, PostgreSQL
seems to incorrectly run it for every row in the table and it takes forever.