[MINOR] cleanup set_session_backend by using pre-computed analysers

Analyser bitmaps are now stored in the frontend and backend, and
combined at configuration time. That way, set_session_backend()
does not need to perform any protocol-specific combinations.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 19d1b04..69505e6 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -150,6 +150,7 @@
 	int state;				/* proxy state */
 	int options;				/* PR_O_REDISP, PR_O_TRANSP, ... */
 	int options2;				/* PR_O2_* */
+	unsigned int fe_req_ana, be_req_ana;	/* bitmap of common request protocol analysers for the frontend and backend */
 	int mode;				/* mode = PR_MODE_TCP, PR_MODE_HTTP or PR_MODE_HEALTH */
 	struct sockaddr_in dispatch_addr;	/* the default address to connect to */
 	union {