Using 2.2 stdlib modules in 2.1

[Gerson Kurz]

If I'm correct, the hmac module was added in 2.2, but is not present
in 2.1 or below. Now, for the next version of shicks! I want to
include SMTP AUTH, and for this I need the hmac module. For 2.2 users
everything is fine, but what if the user has an "older" python
version? (and many, including my webhoster, still do). 

Can I just distribute hmac.py with my BSD-licensed open source app, or
is there a website to point to where you can download lib sources
(hmac.py works without changes in 2.1 and presumably in 2.0 also) so
that I can ask users to manually download it if they need it (which I
think would be a quite bad solution, but still...).