Expose buildCmd

[se7entyse7en]

I don't know how much spread is this need. In my specific case, I need to access the underlying exec.Cmd that is built in buildCmd without starting it. Currently, all the exposed functions that return icmd.Result already started the underlying exec.Cmd.

In case you wonder why I need to do this, here's some context. I need to test an interactive REPL, so I'm using this. The entrypoint of pty is this function:

func Start(c *exec.Cmd) (pty *os.File, err error)

so I'd like to do something like:

r := icmd.BuildCmd(cmd)
in, err := pty.Start(r.Cmd)

[dnephin]

I think it would be nice to be able to use an exec.Cmd directly and still take advantage of the comparison provided by icmd. Sounds like a good idea.