The new std.process is ready for review

[Lars T. Kyllingstad]

Sorry for the delay, but I've pushed a new version now.  There 
are still a few things I haven't done wrt. documentation* and 
unittests**, but the changes to the API and internals should be 
in place.

The biggest changes are that spawnProcess() now closes all 
non-std file descriptors on POSIX systems, and that it handles 
environment variables differently.  Specifically, they are now 
*merged* with the parent's environment by default, rather than 
replacing it.  In addition, there are some things that have been 
renamed, bugs that have been fixed, etc.

> Pull request:
> https://github.com/D-Programming-Language/phobos/pull/1151
>
> Code:
> https://github.com/kyllingstad/phobos/blob/std-process2/std/process2.d
>
> Documentation:
> http://www.kyllingen.net/code/std-process2/phobos-prerelease/std_process2.html


* I'm going to add a function table to the module introduction 
and flesh out the docs for some of the functions a bit.
** spawnShell() currently has no unittest, and I haven't enabled 
the "burn-in" test for Vladimir's escape*() functions yet.