xC/xP: send buffer input history during sync

This transfer is currenly quite simplistic,
but it paves the way for further extensions.

xC.lxdr

@@ -59,6 +59,7 @@ struct EventMessage {
 		BUFFER_RENAME,
 		BUFFER_REMOVE,
 		BUFFER_ACTIVATE,
+		BUFFER_INPUT,
 		BUFFER_CLEAR,
 		SERVER_UPDATE,
 		SERVER_RENAME,
@@ -153,6 +154,9 @@ struct EventMessage {
 		string buffer_name;
 	case BUFFER_ACTIVATE:
 		string buffer_name;
+	case BUFFER_INPUT:
+		string buffer_name;
+		string text;
 	case BUFFER_CLEAR:
 		string buffer_name;