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/blob.c b/src/blob.c
index 58acfc8..6b771fe 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -161,7 +161,7 @@
     if (fwrite(blob->bv_ga.ga_data, 1, blob->bv_ga.ga_len, fd)
 						  < (size_t)blob->bv_ga.ga_len)
     {
-	EMSG(_(e_write));
+	emsg(_(e_write));
 	return FAIL;
     }
     return OK;