ping: Tell SIGQUIT to interrupt the system call

[jlduran]

Summary

Otherwise the statistics won't be printed.
Before:

# ping -4 localhost <PID 1234>
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.001 ms
Quit

In another terminal:

# kill -SIGQUIT 1234

After:

# ping -4 localhost <PID 1234>
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.001 ms

--- localhost ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.001/0.001/0.001/0.000 ms

In another terminal:

# kill -SIGQUIT 1234

Obtained from: Darwin

Test Plan

I don't know how to easily add tests for interrupts, but a simple:

kill -SIGQUIT <PID>

will do.

[asomers]

Philosophically, SIGQUIT is different than SIGINT. It's more like "I the programmer have determined that this program is behaving badly, and would like a core dump". But I could go either way, if people disagree with me here.

[jlduran]

In D38483#875772, @asomers wrote:

Philosophically, SIGQUIT is different than SIGINT. It's more like "I the programmer have determined that this program is behaving badly, and would like a core dump". But I could go either way, if people disagree with me here.

I have added a before/after to the summary. The idea is basically to also dump the statistics, as those could be valuable.

[jlduran]

This revision now gets in the middle of a more important one. Let's abandon it... if there is interest, revisit.