Use stream_socket_recvfrom() in PhpiredisStreamConnection.

Similarly to the socket-ext based connection using phpiredis, in our
stream based PhpiredisStreamConnection class we should read data from
the stream using stream_socket_recvfrom() instead of fread() because
the latter could block until a timeout is reached when the read buffer
contains less data then the specified length.

IMPORTANT: stream_socket_recvfrom() bypasses stream wrappers which
means that TLS/SSL, as requested by PR #158, won't ever work with
this connection class as the function returns the original encrypted
bytes.

This commit fixes issue #180.