Yay!  Please submit your patch using the Patch Manager on SourceForge 
so that we can look at it and discuss it.  You can submit it as one big patch; obviously correct changes can be applied right away causing the patch to shrink, and disentangling the changes shouldn't be too difficult.

The zlib module is really ugly code, and could probably do with a restructuring; I've wondered before if it would be worth trashing it and rewriting from scratch with the same API.  Maybe for 2.2...  If you want to be ambitious and do a more serious restructuring, feel free to do so, but it probably wouldn't get into 2.1.

And the bug has been reclassified under Extension Modules.