source/Tupfile.lua: remove unused file
ThreadControlBlock: implement mechanism of priority changes in
ThreadControlBlock::setPriority() in accordance with POSIX
http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_08_04_02
ThisThread: additional argument for setPriority() to modify ordering
when lowering the priority
test: style fix