Clean up runtime error handling.
Clean up runtime error handling.

This is prep work for being able to catch a runtime error from
another fiber.
minirop/wren,Nelarius/wren,bigdimboom/wren,lluchs/wren,minirop/wren,bigdimboom/wren,foresterre/wren,Rohansi/wren,Nelarius/wren,munificent/wren,Nave-Neel/wren,munificent/wren,daimajia/wren,Rohansi/wren,daimajia/wren,lluchs/wren,foresterre/wren,minirop/wren,daimajia/wren,bigdimboom/wren,munificent/wren,munificent/wren,foresterre/wren,minirop/wren,Rohansi/wren,daimajia/wren,Nelarius/wren,lluchs/wren,Nelarius/wren,Nelarius/wren,munificent/wren,minirop/wren,bigdimboom/wren,Nave-Neel/wren,lluchs/wren,Rohansi/wren,foresterre/wren,Nave-Neel/wren,Nave-Neel/wren,munificent/wren,foresterre/wren