Add Util.sequentialInstance() in support of ceylon/ceylon-compiler#937
Add Util.sequentialInstance() in support of ceylon/ceylon-compiler#937

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