Switch from kill-all-exit to a normal exit when a child is done

[puggan]

see #50

[puggan]

Found out how to reprocude it, and add an test for it.
90a6193

fails in the v1.2.1 and passes in this pr

[freekmurze]

Thanks!

[apibrain]

I found that using exit() here will lead 'mysql has gone away' problem (Even though I reconnect mysql at before child function) , and when I switch back to $this->exit(), all is fine.

I don't test other situations, so I was in doubt about which one is the correct way.

(Environment: PHP 8 + macosx 14)

see also:

• https://www.php.net/manual/en/function.pcntl-fork.php#93466
• https://www.php.net/manual/en/function.pcntl-fork.php#99350