running two independent Cygwin DLLs?

[DJ Delorie]

>     * have a different name, say cygwin1-test.dll, and regenerate the
>       import library accordingly, so that the newly linked apps will 
>       refer to this instead.

Hmmm... Makefile and cygwin.din should do it.  Also change
cygwin.din's BASE to avoid relocation overhead.

>     * change the shared address and name so that the new DLL won't
>       see the values for the stock one.

You'll also need to change some of the version parameters in
winsup/include/cygwin/version.h to use a different shared memory
region and/or other shared resources.  Note that this means that a
parent using one dll will treat a child using the other dll as a
non-cygwin program, and visa versa.