* sigproc.h (set_signal_mask): Remove default on second parameter and make pass

* sigproc.h (set_signal_mask): Remove default on second parameter and make pass
by reference.
* signal.cc (abort): Accommodate change to set_signal_mask.
* select.cc (pselect): Ditto.
* exceptions.cc (handle_sigsuspend): Ditto.
(ctrl_c_handler): Ditto.
(sighold): Ditto.
(sigrelse): Ditto.
(set_process_mask_delta): Ditto.
(_cygtls::call_signal_handler): Ditto.
* fhandler_disk_file.cc (fhandler_disk_file::readdir): Return ENMFILE if
__handle is not set.  Set __handle to NULL when out of files.
(fhandler_disk_file::rewinddir): Don't close handle if it's NULL.
(fhandler_disk_file::closedir): Ditto.