Close the Postscript mode
when archive_ps ne 0, we add the name and the date at the bottom left corner
of the postscript page.
If the postscript is called idl.ps we change its name to number.ps
(number automatically found to be 1 larger that any of the existing ps file)
A long integer giving the id of the information widget (created by openps)
that we have to destroy at the end of closeps (when the postscript is done).