Added t4155 - make sure ^o works in a subdir.

This was broken on OSX since it tup was in a subdirectory when it tried to rename the old outputs.
win32: Ignore paths that start with '\\'

Some programs apparently try to write to \\WMIDataDevice
win32: Ignore writing to the temp directory.

Some programs may write things to the temp directory that aren't tracked and aren't removed when the program completes. Tup should just ignore these.