To stop a lua coroutine, the documentation only mentions yield() ... 
or the
return from the main coroutine function.  But I would like the ability 
to
externally stop or terminate a coroutine.  For example, if I simply 
set the
coroutine variable to nil, will Lua understand to kill the coroutine
(regardless if it is yielded or not) and clean up its stack, all in a
graceful fashion?
Most likely I will attempt this "kill" from C++ rather than from 
within Lua.
But knowing how to address this from lua or C++ would be helpful.