/rebase.sh (was Re: YA call for snapshot testing)

[Andrew Schulman]

> > How should the batch file determine the Cygwin installation location?
> > Just assuming "C:\cygwin" will not work for everyone.
> 
> The batch file could be generated in a postinstall script via sed or gawk.

What's the supported way in a postinstall script to find the Cygwin
installation directory?  I thought of 'cat
/proc/registry/HKEY_CURRENT_USER/Software/Cygwin/something-or-other', but
it seems that there can be multiple installation locations stored there.