A small convenience update to OSProcess/CommandShell

> I have updated OSProcess/CommandShell with some changes that allow
> PipeableOSProcess to be used more conveniently for executing commands on
> a Unix/Linux/OSX system. You can now run a simple command without worrying
> about closing (pipe) file handles or other special handling. For example:
>
>      ( PipeableOSProcess command: 'ls -l' ) output
>
> Explanation: PipeableOSProcess was originally designed to support command
> pipeline execution within a CommandShell. In that scenario, the command shell
> handles all setup and cleanup of pipe handles. In practice, PipeableOSProcess
> turns out to be useful for simple command execution with input and output
> pipes connected to the image. The updates to PipeableOSProcess class>>command:
> add the necessary setup and cleanup that would otherwise have been done by
> the command shell.
>
> OSProcess and CommandShell are on SqueakMap (select the "head" version to
> get the latest), or from the squeaksource repository at:
>
>   http://www.squeaksource.com/OSProcess
>   http://www.squeaksource.com/CommandShell
>
> Dave
>
>