Ned: the new functionality is also needed for 2-way univeral binaries, it makes pythonw behave much more as if you execute the real interpreter instead of a stub executable.

That posix_spawn doesn't exist sucks, and I'm a bit annoyed with myself for not noticing that before the commit. 

It is pretty easy to create executables on 10.5 that use posix_spawnv when available using weak linking (we already do that in posixmodule.c for other functionality).

That won't work for builds on 10.4, or linking to the 10.4u SDK, if the posix_spawn symbols aren't present there: weak linking still has to resolve the symbol at link-time and only ensures that the executable won't fail to start when the symbol isn't present at runtime.

I don't have the 10.4u SKD on my machine at the moment and cannot investigate further at the moment, but will do ASAP.

Another thing I'd like to do before 2.7 is released is to see if it is possible to perform the build using the default SDK and patch distutils to use the 10.4u SDK when building extensions for a universal build on a n OSX 10.4 system (because the default SDK on those systems cannot build  universal binaries).