fuser: code shrink, fixing default signal, exitcode and PID display

fuser: code shrink, fixing default signal, exitcode and PID display

Defult signal is KILL, not TERM.
We used to not display PIDs with -k but without -s, but
upstream (fuser from PSmisc 22.7) still shows PIDs.
Filtering out of our own PID was buggy.

function                                             old     new   delta
fuser_main                                           669     918    +249
search_dev_inode                                      67      74      +7
add_pid                                               38      39      +1
scan_pid_maps                                        225     222      -3
add_inode                                             91      88      -3
packed_usage                                       27047   27039      -8
scan_dir_links                                       102      76     -26
scan_link                                             78      46     -32
file_to_dev_inode                                     64       -     -64
scan_proc_net                                        307       -    -307
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 3/5 up/down: 257/-443)         Total: -186 bytes

Signed-off-by: Maksym Kryzhanovskyy <xmaks@email.cz>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>