RFC: fake fork on Unix

There's a 5.16-blocking bug in Win32 fork emulation, that was tickled
by a change I made, and which I'm not equipped to fix because I have no
Win32 machine on which to reproduce the fault.  I propose that the Win32
fake fork should be made available *to the core test suite* on *all*
platforms (when built for threading), and that the fork tests should
be run with both the real fork and the fake fork.  This would provide
quicker detection of bugs and easier debugging.

-zefram

• RFC: fake fork on Unix by Zefram
• Re: RFC: fake fork on Unix by Ricardo Signes
• Re: RFC: fake fork on Unix by Nicholas Clark