popen: raise an error on NaN as a timeout or a signal number

[Totktonada]

Timeouts in popen are not checked against NaN.

The following methods accept NaN as a timeout and it works like an infinity timeout.

ph:wait({timeout = 0/0})
ph:read({timeout = 0/0})
ph:write({timeout = 0/0})

They should raise IllegalParams error.

It also worth to verify a signal number against NaN. Now it returns nil, err, where err is SystemError.

ph:signal(0/0)
---
- null
- Unable to killpg 18109 signo -2147483648: Invalid argument
...

It should raise IllegalParams error.