Creating CVS diffs

I'm currently building a site, which will hopefully eventually come a rather complicated Drupal implementation. The site will use at least the following modules in addition to Drupal core: Taxonomy Access Control, Taxonomy Browser, Image, HTMLArea, SiteMap or SiteMenu, Attachment, Event and Remindme. The site will run on PostgreSQL, and will actually include two separate sites using database prefixes and shared user tables. It will probably be based on 4.5.2, as 4.6 RC still generates way too much errors on Postgres, and the availablility of modules is also still poor.

Because it seems that many of the modules and even some features of the core (so far locales.inc and aggregator.module have required fixes) are not really developed with PostgreSQL in mind, I've found quite a lot of functionality that generates SQL errors (especially the amount of incomplete GROUP BY clauses is rather incredible) and needs to be fixed before it can actually be used.

While I'm not a real programmer, I know enough SQL to be able to fix those errors. But due to my lack of programming background, I've no idea how to create cvs.diffs of them to share my fixes with drupal community, which I'd be glad to do.

Now, supposing that I've an original file and the equivalent file fixed by me, can anyone point me an easy way to properly create CVS diffs from them?