ACE::writev_n with iovecs that have been allocated on the heap.
In case of a partial send, libACE will loop until all the data has been
sent. The problem is that it updates its arguments when doing so,
leaving the caller with one or more updated pointers inside the table of
iovecs. Attempting to free such a pointer results in a fault (the value
can even not be aligned properly).
The fix simply copies the iovec data _if necessary_ (no perf penalty
otherwise), and updates those values instead of the arguments.