BUG/MEDIUM: connections: Don't forget to remove CO_FL_SESS_IDLE.

If we're adding a connection to the server orphan idle list, don't forget
to remove the CO_FL_SESS_IDLE flag, or we will assume later it's still
attached to a session.

This should be backported to 1.9.
diff --git a/include/proto/session.h b/include/proto/session.h
index 0b7d08d..f1e33fa 100644
--- a/include/proto/session.h
+++ b/include/proto/session.h
@@ -128,7 +128,8 @@
 			/* The server doesn't want it, let's kill the connection right away */
 			conn->mux->destroy(conn);
 			return -1;
-		}
+		} else
+			conn->flags &= ~CO_FL_SESS_IDLE;
 		return 1;
 	} else {
 		conn->flags |= CO_FL_SESS_IDLE;