Custom release node validation not happening

I just discovered a nasty bug introduced in #390856: Do a proper page/code split of project. The project_release_node_form_validate() validation callback for the release node form is not getting called since it lives in an include file. I thought that hook_form() would be getting invoked, which loads the include file that this validation callback lives in. But, apparently that's not the case (presumably because the form is already built and cached). So, the validation callback is just silently ignored. Evil.

I could move the (large) function back into project_release.module, but I'd rather find a more sane way to deal with this. I'll check with chx in IRC and see what we can come up with...