MSVCRT's _wrename() cannot rename symlinks over existing files: it returns
success without doing anything. Newer MSVCR*.dll versions probably do not
have this problem: according to CRT sources, they just call MoveFileEx()
with the MOVEFILE_COPY_ALLOWED flag.
Get rid of _wrename() and call MoveFileEx() with proper error handling.
Signed-off-by: Karsten Blees <blees@dcon.de>