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.
error: pretxncommit.nocommits hook failed: no commits allowed
abort: no commits allowed
transaction abort!
rollback completed
error: pretxncommit.nocommits hook failed: no commits allowed
abort: no commits allowed
transaction abort!
rollback completed