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.
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
verify failed
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
commit failed
diff -r c1fab96507ef a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@ foo
-foo
+barber