Fix segfaults with Popen4 and Ruby 1.8.7

When using Ruby 1.8.7 with Popen4 ruby regularly segfaults.

This is a well-known work around for that issue.

I was able to easily reproduce this issue on: 
* Ubuntu 12.04 +  ruby 1.8.7 (2011-06-30 patchlevel 352) [x86_64-linux]
* Take a dump that lasts a couple minutes, GC will come around and segfault your face!

See: 
http://tickets.opscode.com/browse/CHEF-2916
https://github.com/engineyard/engineyard/issues/115