As far as I can tell all of these files have no matching entry in Make.config.objects and are not actually compiled at build time.
Rather than keeping these uncompiled files around in the repo I think we should remove them since they make the code harder to understand and because people might be tempted to edit them or make decisions about the codebase based on grep results.
If any of these are supposed to be kept around for reference or because they're supposed to be compiled but are not because of a bug, let me know and I'll add them back. Please also let me know if anyone has a problem with doing this sort of dead code cleanup.
I'm super in favor. The existence of two SetExternalBoundary source files has wasted more than one person's time. Thanks!
passes the test suite (unsurprisingly) on revision 1fcd36a. Thanks for cleaning up the codebase, @ngoldbaum - it's appreciated!