r2660: - converted the libcli/raw/ library to use talloc_increase_ref_count()

r2660: - converted the libcli/raw/ library to use talloc_increase_ref_count()
  rather than manual reference counts

- properly support SMBexit in the cifs and posix backends

- added a logoff method to all backends

With these changes the RAW-CONTEXT test now passes against the posix backend
(This used to be commit c315d6ac1cc40546fde1474702a6d66d07ee13c8)