r2569: Patch from Rob Foehl <rwf@loonybin.net>:

r2569: Patch from Rob Foehl <rwf@loonybin.net>:

- fix typo in libads/ldap_printer.c:39, ads_find_printer_on_server()
  (originally libads-typo.patch)
- fix leak in printing/nt_printing.c, is_printer_published()
  (originally is_printer_published-leak.patch)
- fix double print_backend_init() calls, now only called from main()
- restructuring in printing/nt_printing.c
  - replaced (un)publish_it() with ads-specific functions
  - moved common code to nt_printer_publish()
  - improved error handling in several places
- added check_published_printers() in printing/nt_printing.c, to verify
  that each published printer is actually in the directory at startup
- changed calling semantics of mod_a_printer, dump_a_printer, and
  update_driver_init to be more consistent with the rest of the api and
  reduce some copying