timeout*1000 is harmful!

[Demetrio92]

I don't know whether this also affects windows users, but the sys call to ping on linux is executed with timeout * 1000 passed to -W argument. My man ping (ubuntu 16.04) says:

       -W timeout
              Time to wait for a response, in **seconds**. The option affects only timeout in 
              absence of  any responses, otherwise ping waits for two RTTs.

Therefore calling ping('lalala.com') dead-locks the R session (ok, actually, only affects Rstudio, and not the terminal, but nonetheless).
The documentation does not say anything about the measurement units, and the default for timeout argument is set to 1,

IMO, two things should be changed:

1. Documentation should be clear about the units
2. The default should be max 10 seconds

[gaborcsardi]

The dead lock will be solved by #8. Sadly, it seems that different ping programs take different units, so I would need to rewrite the ICMP ping in C: #11.

Btw. there is a new is_up() function, and I guess people would need that more often than ping().

[gaborcsardi]

Nevertheless if looks like Linux has the timeout in seconds, so I can do that change already now.