MOVE commands fail on some broken web servers when overwriting

MOVE commands that will result in an existing file being overwritten are issued without the Overwrite header being explicitly set. This complies with the RFC, as compliant servers must assume a value of T if the Overwrite header is absent.

Some paranoid non-complaint servers, however, will refuse to overwrite an existing file unless you explicitly set the Overwrite header to T, totally breaking pushes as-is. There isn't any real downside to sending the extra header, even when it isn't needed, and it will improve compatibility.