MEDIUM: threads/lua: Makes the jmpbuf and some other buffers local to the current...

MEDIUM: threads/lua: Makes the jmpbuf and some other buffers local to the current thread.

The jmpbuf contains pointer on the stack memory address currently use
when the jmpbuf is set. So the information is local to each thread.

The struct field is too big to put it in the stack, but it is used
as buffer for retriving stats values. So, this buffer si local to each
threads. Each function using this buffer, use it whithout break (yield)
so, the consistency of local buffer is ensured.