MAJOR: connection : Split struct connection into struct connection and struct conn_stream.

All the references to connections in the data path from streams and
stream_interfaces were changed to use conn_streams. Most functions named
"something_conn" were renamed to "something_cs" for this. Sometimes the
connection still is what matters (eg during a connection establishment)
and were not always renamed. The change is significant and minimal at the
same time, and was quite thoroughly tested now. As of this patch, all
accesses to the connection from upper layers go through the pass-through
mux.
diff --git a/include/proto/stream.h b/include/proto/stream.h
index 3efb42b..f0edc2e 100644
--- a/include/proto/stream.h
+++ b/include/proto/stream.h
@@ -36,7 +36,7 @@
 extern struct data_cb sess_conn_cb;
 
 struct stream *stream_new(struct session *sess, enum obj_type *origin);
-int stream_create_from_conn(struct connection *conn);
+int stream_create_from_cs(struct conn_stream *cs);
 
 /* perform minimal intializations, report 0 in case of error, 1 if OK. */
 int init_stream();