If part of your purpose for posting code is for others to send you fixes, then it will help greatly to embed a file version stamp in each file. That provides a way for people to do a quick check to see if the module they just reviewed or extended has been updated, and it provides you with a quick check to see if submitted code is based on older versions of files. Any decent source-code control system will provide a way to embed a version string in a file.

Your cause is also going to be helped by having a complete test suite corresponding to each package you're publishing. You can then enforce that any submissions need to pass the published tests, and that any newly submitted functionality needs to be covered by new tests. It also provides a backstop to help prevent your posting broken code.