convert: workaround for cvsps.cache under Windows
In non-cygwin environment, cvsps fails to create its cache directory and redirect its output to stderr. Just ignore the error and capture stderr as well.
adding baradding foo% state dumpa 644 0 bazn 644 0 foor 0 0 bar% statusA bazR barC foo% state dumpn 666 -1 barn 666 -1 foo% status! bar? bazC foo