Use Kernel.spawn instead of system

[jalcine]

Just to prevent the holding up of Guard from running other guards; it'd be dope if this didn't use system but used Kernel.spawn instead.

[sethk]

I would like to have this as well, and of course it would need to avoid running concurrently.

[jalcine]

Ah so you'd want this to ensure serial execution of guards. That makes sense.

We could take that PID and then use Process.wait on it.

P.S: A year later! </3. I still use Guard a lot so this means a lot.