Add missing LM_ prefixes.

diff --git a/src/lingot-gui-mainframe.c b/src/lingot-gui-mainframe.c
index 8380406..97d2893 100644
--- a/src/lingot-gui-mainframe.c
+++ b/src/lingot-gui-mainframe.c
@@ -239,12 +239,12 @@ gboolean lingot_gui_mainframe_callback_error_dispatcher(gpointer data) {
 							GTK_WINDOW((frame->config_dialog
 											!= NULL) ? frame->config_dialog->win : frame->win),
 							GTK_DIALOG_DESTROY_WITH_PARENT,
-							(message_type == ERROR) ? GTK_MESSAGE_ERROR
+							(message_type == LM_ERROR) ? GTK_MESSAGE_ERROR
 									: ((message_type == LM_WARNING) ? GTK_MESSAGE_WARNING
 											: GTK_MESSAGE_INFO),
 							GTK_BUTTONS_CLOSE, error_message);
 			gtk_window_set_title(GTK_WINDOW(message_dialog), (message_type
-					== ERROR) ? _("Error")
+					== LM_ERROR) ? _("Error")
 					: ((message_type == LM_WARNING) ? _("Warning") : _("Info")));
 			gtk_window_set_icon(GTK_WINDOW(message_dialog),
 					gtk_window_get_icon(GTK_WINDOW(frame->win)));