std.process.system and friends

[HeiHon]

> Hmmm, AFAIK it is outdated, isn't it ? I also hesitate to 
> introduce
> major dependencies for this small point.

It was originally for D1, but SiegeLord ported almost all of it 
to D2.

> Can you point me to the sources of this Tango version please.
> May be I can reuse a small part of it.

https://github.com/SiegeLord/Tango-D2

There are still some very useful things in Tango that you don't 
find in Phobos (e.g. logging) and it plays nicely together with 
Phobos.