lib/select.c: Fix for Linux 2.0.x kernel that causes select to return true on a pipe

lib/select.c: Fix for Linux 2.0.x kernel that causes select to return true on a pipe
                and then a blocking read to fail. Make the pipe read/write non blocking.
printing/printing.c: Added a mutex around the code that enumerates all the jobs in a
                    print queue. Allows only one smbd to be doing this at any one time.
                    This fixes a capacity problem discovered at HP with <10,000 jobs in
                    a print queue.
Jeremy.