Chat's buffer handling:

Chat's buffer handling:
 - Fixed bug with unchecked out-of-mem conditions
   while reading client request & server headers
 - No longer predict if the buffer limit will be exceeded
   in the next read -- check add_to_iob's new
   return code. If buffer couldn't be extended
   (policy or out-of-mem) while
   - reading from client: abort
   - reading server headers: send error page
   - buffering server body for filter: flush,
     and if that fails: send error page