Rather than answering your question directly (since I suspect the answer is that the wiki needs a configuration tweak): for source code, wouldn't it be more appropriate to upload it to someplace like github.com, code.google.com, bitbucket.org, etc? That gives others the opportunity to fork it, make changes, submit improvements back to you, etc.
It's much more useful to be able to browse and search the source online via a web browser (as on one of those sites) than to stop what you're doing to download and extract a zip file, find room for it if needed, and manually paw through the result to see what you're looking for.
I see a lot of folks who, even when they upload source to code.google.com, just upload a zip file or tarball, instead of using source control. I must admit, I'm a little confused by that.