Added a check to prevent non-CLI calls from failing.

[im-bryan]

When using this package in a script that isn't called through the CLI, there is a big chance that the functions defined in the PCNTL package aren't available, because of obvious security implications.

Because of the fact that the pcntl_signal closure is set in the constructor of the RedisSimpleLock, this class is unusable when used through different measure than the PHP CLI.

This PR makes sure that the closure is only attached when the CLI is used.

[mathroc]

thx @im-bryan for this PR, this is something that was already requested and I didn't have time to work on ( see #6 )

[im-bryan]

@mathroc I changed some stuff around. You can now explicitly ignore specific SAPIs when instantiating the RedisSimpleLock. I've also included tests to prove the feature is working as intended.

[mathroc]

awesome thank you !

it looks ready for me, let me know if it's ok to merge for you and I 'll do it and release a new version

[im-bryan]

@mathroc I don't have anything left to do. So I'd be very happy if you could merge it in.
The only thing I'm not happy with is that pcntl_signal_get_handler was introduced in version 7.1 of PHP so the tests only actually test this feature through PHPUnit in PHP 7.1 and up. AFAIK I cannot really get information about registered signals without this function, so PHP7.0 and down.

[mathroc]

that's fine with me, it's not fully tested on <=7.0 but those versions of php are not supported anymore anyway ( https://www.php.net/supported-versions.php )

and that's relatively straightforward so testing it on 7.1+ is most likely enough