client: add local_protocol_name binding to info

In the case you are creating a client connection, there may be
no relationship between the ws protocol you want to bind to at
the server, and the local protocol name you want the wsi to
bind to at the client.

This introduces a new client info struct member .local_protocol_name,
if it is NULL then all is as before, otherwise it binds the client
wsi to the named protocol early in the process, and .protocol is used
for the negotiation with the ws server.

This allows you to bind client wsi to local protocol handlers that
don't share the name of the ws protocol the connection will try
to negotiate.