Revert "Use exclusive mode by default unless within a task"
Revert "Use exclusive mode by default unless within a task"

This change is causing sporadic hangs and seems to be setting @exclusive
inappropriately. It needs to be investigated further.

This reverts commit 6328c9f9691e83d58f61b98121cd3ab58622732b.

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