posix_spawn only dup2() once

[leorize]

The program pipe.c attempts to redirect pipetest.c stdout and stderr to their respective pipes for inspection

How to run:

$ gcc -o pipetest pipetest.c
$ gcc -o pipe pipe.c
$ ./pipe

Expected: no output

Got:

test err

(hangs)

The hang happens because the child stderr isn't redirected to the pipe.

Tested on hrev52165, x86_64

[korli]

Fixed in hrev52177. Thanks for the report!