How do I create a potential shippable product (PSP) at the end of a sprint?

Question

I'm running a team of 4 developers and 2 testers and trying to abide by the Scrum principle of creating a PSP with every sprint. That means I need to create a potential release with all the user stories that got to Done and store it on some publish server for the PO to do with as they please.

My problem is how to technically create the build when some stories are not at Done at the end of the sprint? The code is checked in, but didn't completely pass testing.

If I only check-in code that is Done, i.e. code complete-reviewed-tested, I run in to the possibility of diverging code bases and merges that may be disastrous. For instance Developers A and B work on different features that modify assembly X. Dev A finishes coding, pushes assembly X to test. The next day Dev B finishes coding and pushes assembly X to test. Feature A comes back with bugs, feature B is perfect. Oops, sprint is over. Now, how do I create a PSP with feature B but not A?