Internal variable changes to defcustom,

Internal variable changes to defcustom,
make-local-hook changes to defvar.  Doc fix.
(ps-print-version): New version number (6.1).
(ps-setup, ps-do-despool): Code fix.
(ps-printer-name): Customization fix.
(ps-printer-name-option): Now is a defcustom instead of an
internal variable.
(ps-print-hook, ps-print-begin-sheet-hook, ps-print-begin-page-hook)
(ps-print-begin-column-hook): Now are defvar instead of
make-local-hook.