//
// On Windows it wraps os.Rename, which (as of 2019-06-04) uses MoveFileEx with
// MOVEFILE_REPLACE_EXISTING.
//
// Windows also provides a different system call, ReplaceFile,
// that provides similar semantics, but perhaps preserves more metadata. (The
// documentation on the differences between the two is very sparse.)
//
// Empirical error rates with MoveFileEx are lower under modest concurrency, so