Unable to use Cygwin RCS commands in Windows Emacs

[Heinz Werner Kramski-Grote <kramski@web.de>]

At some point in history, /usr/bin/co, /usr/bin/ci, /usr/bin/rlog etc. turned 
from .exe into shell scripts, which are now wrappers for the main program 
/usr/bin/rcs.exe. 

However, these shell scripts can not be called directly from a Windows command 
line and moreover can not be invoked by a Windows (not Cygwin) Emacs (25.2 
currentlly).

Windows Emacs expects external Windows commands/binaries like co, ci, rlog, 
etc.  to exist somewhere in the PATH. The commands to be invoked for version 
control with RCS are hardcoded into "C:\Program Files\emacs-25.2\share\emacs
\25.2\lisp\vc\vc-rcs.el" and can not be customized, as far as I know.

I tried to create wrapper scripts for Windows too (co.cmd, ci.cmd etc. -  
basically just "c:\cygwin\bin\bash -c '/bin/%~n0 %*'"), which work to some 
extend on the Windows command line, but mostly fail when invoked from Emacs' 
version control functions.

The most recent native Windows port of RCS I could find is version 5.7 and 
dates back to 1999. In addition, it uses filenames like "RCS/somefile" instead 
of the usual "RCS/somefile,v", so this does not look like a way to go either. 

I'm clueless now. Does someone successfully use Cygwin's RCS commands in 
Windows Emacs? Is there still an older Cygwin RCS package around which 
contains "real" co.exe, ci.exe etc.? 

Any help is greatly appreciated.
   Heinz

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