[MINOR] http: introduce a new synchronisation state : HTTP_MSG_DONE

This state indicates that an HTTP message (request or response) is
complete. This will be used to know when we can re-initialize a
new transaction. Right now we only switch to it after the end of
headers if there is no data. When other analysers are implemented,
we can switch to this state too.

The condition to reuse a connection is when the response finishes
after the request. This will have to be checked when setting the
state.
diff --git a/include/types/proto_http.h b/include/types/proto_http.h
index 2fa0d59..c5d48d3 100644
--- a/include/types/proto_http.h
+++ b/include/types/proto_http.h
@@ -181,6 +181,8 @@
 #define HTTP_MSG_DATA_CRLF    31 // skipping CRLF after data chunk
 #define HTTP_MSG_TRAILERS     32 // trailers (post-data entity headers)
 
+/* we enter this state when we're done with the current message */
+#define HTTP_MSG_DONE         33 // message done, waiting to resync for next one.
 
 /* various data sources for the responses */
 #define DATA_SRC_NONE	0