Upside-down and face background color printing,

Upside-down and face background color printing,
line number step, doc fix.
(ps-print-version): New version number (5.2).
(ps-setup, ps-prologue-file, ps-begin-file, ps-begin-job)
(ps-face-attribute-list, ps-plot-with-face): Code fix.
(ps-spool-config): Var fix.
(ps-printer-name-option): Const fix.
(ps-print-upside-down, ps-use-face-background,
ps-line-number-step): New vars.
(ps-window-system, ps-lp-system): New consts.
(ps-face-background): New fun.