* lisp/lpr.el: Signal print errors more prominently.

* lisp/lpr.el: Signal print errors more prominently.
(print-region-function): Don't default to nil.
(lpr-print-region): New function, extracted from print-region-1.
Check lpr's return value and signal an error in case of problem.
(print-region-1): Use it.
* lisp/ps-print.el (ps-windows-system, ps-lp-system): Remove.  Use the lpr-*
versions instead.
(ps-printer-name): Default to nil.
(ps-printer-name-option): Default to lpr-printer-switch.
(ps-print-region-function): Don't default to nil.
(ps-postscript-code-directory): Simplify default.
(ps-do-despool): Use lpr-print-region to properly check the outcome.
(ps-string-list, ps-eval-switch, ps-flatten-list)
(ps-flatten-list-1): Remove.
(ps-multibyte-buffer): Avoid setq.
* lisp/dos-w32.el (direct-print-region-helper): Use proper regexp operators.
(print-region-function, ps-print-region-function): Don't set them here.