workaround MRI bug in preserving exit status in at_exit
workaround MRI bug in preserving exit status in at_exit

http://bugs.ruby-lang.org/issues/5218

davydovanton/celluloid,dilumn/celluloid,TiagoCardoso1983/celluloid,seuros/celluloid,mehta/celluloid,sideci-sample/sideci-sample-celluloid,kenichi/celluloid,olleolleolle/celluloid,jasonm23/celluloid,celluloid/celluloid,marshall-lee/celluloid,tarcieri/celluloid,jstoja/celluloid