code review 6711043: present: fix another race condition

present: fix another race condition
Several bad things are posible.
1. Since c.run() is executed in a separate goroutine,
c.kill() can find c.cmd==nil. If so, it won't kill the process,
but will wait for it's completion. Deadlock.
2. c.kill() can "kill" already completed "go build" process,
but then wait for completion of the compiled binary. Deadlock once again.

With this change it's impossible to kill "go build" process,
but it must not hang, right?

[dvyukov, 2012-10-16 06:54:37]

Hello adg@golang.org (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://dvyukov%40google.com@code.google.com/p/go.talks/

[adg, 2012-10-16 22:10:54]

Thanks for the fix, but I don't really like threading the inited channel through
those functions. I've restructured the code a little here:

https://codereview.appspot.com/6719050

I'd love it if you would run your manual race detector over it ;)