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/proto/digraph.pro b/src/proto/digraph.pro
index 37dc2b2..06b3341 100644
--- a/src/proto/digraph.pro
+++ b/src/proto/digraph.pro
@@ -5,7 +5,7 @@
 int getdigraph(int char1, int char2, int meta_char);
 void putdigraph(char_u *str);
 void listdigraphs(int use_headers);
-char_u *keymap_init(void);
+char *keymap_init(void);
 void ex_loadkeymap(exarg_T *eap);
 void keymap_clear(garray_T *kmap);
 /* vim: set ft=c : */