[incompatible] killall child processes when sending SIGKILL on Unix systems

[Songmu]

To reduce the probability of an orphan process occurring

[coveralls]

Coverage increased (+2.0%) to 62.343% when pulling 7e3e8b1 on kill-kill-child-processes into d2f1bf0 on master.

[coveralls]

Coverage increased (+1.8%) to 62.185% when pulling 64258f4 on kill-kill-child-processes into d2f1bf0 on master.

[coveralls]

Coverage increased (+1.8%) to 62.185% when pulling a1f36ad on kill-kill-child-processes into d2f1bf0 on master.

[coveralls]

Coverage increased (+1.8%) to 62.185% when pulling a1f36ad on kill-kill-child-processes into d2f1bf0 on master.

[coveralls]

Coverage increased (+1.8%) to 62.185% when pulling 31e10dc on kill-kill-child-processes into d2f1bf0 on master.