Use getmypid() instead of posix_getpid()

[aschempp]

Any reason not to?
http://stackoverflow.com/questions/1176012/difference-between-getmypid-and-posix-getpid

This applies at least to the RunTaskCommand.

[discordier]

Nope, no reason against doing so.

We most likely will have to rework some of this stuff for Windows support anyway, therefore I'll flag it as enhancement.