[echo_client] Exit when an extension is enabled and an old protocol which does not support extensions is specified
[echo_client] Exit when an extension is enabled and an old protocol which does not support extensions is specified

Release note: Exit echo_client when an extension is enabled and an old protocol is specified.

Review URL: https://codereview.appspot.com/9072043

git-svn-id: d23f85197b9dafcb1b1682eb9d0eda70517bdc52@767 4ff78f4a-9131-11de-b045-6380ec9940d4

bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src