Message 150004 - Python tracker

> There is probably lots of such code:

> I'm not convinced about making it the default behaviour, and 
> certainly not the only one.

Then I'm not convinced that this patch is useful.
Having three different implentations and code paths doesn't sound like a good idea to me.
fork() vs fork() + exec() is an implementation detail, and exposing such tweakables to the user will only make confusion worse.