patch 8.1.0743: giving error messages is not flexible

Problem:    Giving error messages is not flexible.
Solution:   Add semsg().  Change argument from "char_u *" to "char *", also
            for msg() and get rid of most MSG macros. (Ozaki Kiichi, closes
            #3302)  Also make emsg() accept a "char *" argument.  Get rid of
            an enormous number of type casts.
diff --git a/src/gui_beval.c b/src/gui_beval.c
index b3d8e6c..9af17a9 100644
--- a/src/gui_beval.c
+++ b/src/gui_beval.c
@@ -103,7 +103,7 @@
 
     if (mesg != NULL && mesgCB != NULL)
     {
-	IEMSG(_("E232: Cannot create BalloonEval with both message and callback"));
+	iemsg(_("E232: Cannot create BalloonEval with both message and callback"));
 	return NULL;
     }