Replace primitive typecasts with bounds-checked conversion in Util (see ceylon/ceylon-compiler#1559).
Replace primitive typecasts with bounds-checked conversion in Util (see ceylon/ceylon-compiler#1559).

jvasileff/ceylon.language,jvasileff/ceylon.language,lucaswerkmeister/ceylon.language,lucaswerkmeister/ceylon.language,ceylon/ceylon.language,unratito/ceylon.language,unratito/ceylon.language,ceylon/ceylon.language