BUG/MEDIUM: hlua: Report to SC when output data are blocked on a lua socket

BUG/MEDIUM: hlua: Report to SC when output data are blocked on a lua socket

It is a fix similar to the previous one ("BUG/MEDIUM: hlua: Report to SC
when data were consumed on a lua socket"), but for the write side. The
writer must notify the cosocket it needs more space in the request buffer to
produce more data by calling sc_need_room(). Otherwise, there is nothing to
prevent to wake the cosocket applet up again and again.

This patch must be backported as far as 2.8, and maybe to 2.6 too.