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 dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)