[PATCH] implement stream_set_write_buffer for sockets

Hello, Currently stream_set_write_buffer() only works with file streams. If used on socket streams it always returns -1 and does nothing. This can be quite problematic when using datagram sockets because any datagram bigger than the default 8Kb gets chopped and more than one datagram get sent, eventually messing up with the receiving side. This small patch adds support for sockets in stream_set_write_buffer(), I have tested it and it fixed my problem, but if it needs refinements i'd be glad to try and help more. diff against 5.2.5 is here: http://rectophobia.com/~six/socket_write_buffer.diff Regards, Vincent