Avoid collisions between parallel installations of Cygwin

[Earnie Boyd]

Quoting Corinna Vinschen <corinna-cygwin@cygwin.com>:

>
> Last, but not least, there's always a chance that somebody tries to exec
> a Cygwin process from the /bin directory of another Cygwin installation.
> This will result in loading "the other" Cygwin DLL for the child
> process.  Tricky, given that this requires process interaction, while
> the whole idea of the change is to avoid interaction.  So this case is
> still not supported and the result is not determined.  It might work,
> but you can also easily see the friendly "multiple Cygwin" error message
> instead.  The rule is, keep separate Cygwin installations separate.
>

This is what MSYS does as well.  Executing from a different /bin  
directory will usually cause a process hang.  But, I think about only  
one user has ever tried that and that user would be me.  BTW, I took  
the idea from Cygwin itself which allowed for multiple Cygwin with one  
being in DEBUGGING mode.  I just expanded that idea.

> Per the contract, the patch has been fully tested in a test environment,
> including test protocol, so I'm pretty confident that it works as
> advertised.
>

This is really cool.  I am glad to hear that Cygwin is doing this.

--
Earnie