exec: Add WaitTimeout

[FlorianUekermann]

Feature Request:

Add Cmd.Wait() like function in exec with timeout.
Behavior should resemble Wait() as close as possible, but the corresponding process is
killed after the specified time elapsed.

Suggested Prototype:

func (cmd *Cmd) WaitTimeout(ns int64) (os.Error)

[FlorianUekermann]

Comment 1:

Changes are more or less trivial I think, and since I needed it today anyway, I uploaded
it and sent review request it to bradfitz.
http://golang.org/cl/4530108

[adg]

Comment 2:

Owner changed to @bradfitz.

Status changed to Accepted.

[rsc]

Comment 3:

No Timeout methods please.

Status changed to Invalid.

[FlorianUekermann]

Comment 4:

I think we all agree now that introducing additional methods is a bad thing to do. If
you object to timeouts in general, you might want to take a look at the CL.