Work around leftover temporary save file.

Work around leftover temporary save file.

If a file exists and is hidden on Windows the Tcl open command will
fail as the attributes provided in the CREAT call fail to match those
of the existing file. Forcing removal of the temporary file before we
begin solves any problems caused by previous failures to save the
application settings. An alternative would be to remove the hidden
attribute before calling 'open'.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>