process: Confusion about UseHandle handles being closed.

[Henning Thielemann]

On Tue, 25 Nov 2014, Michael Snoyman wrote:

> 1. Add clear documentation to `createProcess` indicating that it will close the `Handle` automatically.
> 2. Add a new function to be exported from `System.Process` with the semantics of `createProcess_`. I'm open
> to bikeshedding on the name, but perhaps sticking with `createProcess_` makes the most sense.

I think the cleanest solution would be to add a new field (e.g. leaveOpen) 
to the CreateProcess record. (Btw. why are the other fields named with 
underscores?) Otherwise, every new switch to createProcess multiplies the 
number of its variants. Users who create the CreateProcess structure using 
'shell' and 'proc' won't need to adapt their code.