This looks like it simplifies mutex handling a lot. I haven't investigated in great detail but since you've provided some test cases, feel free to check in.
I tried but it seems that my ssh login is no longer valid, i get:
cvs -z9 -d :ext:[EMAIL PROTECTED]:/cvs/src co src
Permission denied.
cvs [checkout aborted]: end of file from server (consult above messages if any)
