SPDY: replace exception in SpdyHeaderBlockZlibEncoder with EMPTY_BUFFER
Adds port to the host header value in WebSocket client handshake.

Due to http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.23 the port should be added if it differs from the default port. To simplify the code we just always add the port.

Backported from 82176bed76ddca1506a3627a7804d51f00637186