If you're not running gclient sync with --verbose and you get a conflict on
a file, the conflict message prints *before* the message that you're running
update in the appropriate directory. This is happening because we intercept
stdout but not stderr, and the conflict prompt goes to stderr. redirecting
stderr in the popen() to the pipe fixes this.

  R=maruel@chromium.org
  BUG=none
  TEST=none

Review URL: http://codereview.chromium.org/373003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@31276 0039d316-1c4b-4281-b951-d872f2087c98