Reverse dependencies for popen4

Latest version of the following gems require popen4

Gem	Version	Date	Downloads
vbox +4.73 Thousand Downloads	`0.0.4` November 28, 2011	November 28, 2011	4.73 Thousand
task-orchestrator.gemspec +4.33 Thousand Downloads	`0.0.1` January 07, 2013	January 07, 2013	4.33 Thousand
cloudscale-benchmark +4.33 Thousand Downloads	`0.0.2` October 13, 2014	October 13, 2014	4.33 Thousand