MEDIUM: threads/lua: Cannot acces to the socket if we try to access from another...

MEDIUM: threads/lua: Cannot acces to the socket if we try to access from another thread.

We have two y for nsuring that the data is not concurently manipulated:
 - locks
 - running task on the same thread.
locks are expensives, it is better to avoid it.

This patch cecks that the Lua task run on the same thread that
the stream associated to the coprocess.

TODO: in a next version, the error should be replaced by a yield
and thread migration request.