Fix timeout and bufsize for hack with real_sendall method

Hi, 

I  face a problem. My test hangs when httpretty uses `real_sendall` method as a proxy to real network socket. I hacked `real_sendall` method and found that very small buffer size used for receiving data from real socket. A receiving speed with buffer of 16 bytes is very-very-very slow. A timeout for real socket is set to zero. So test is stopped for very long time. 

Please, accept my changes, if you find it is correct. They are usefull for me. But I don`t understand why timeout=0 and bufsize=16 were used and I suspect you may have a reasonable reason to do so.

Thanks in advance!