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/crypt.c b/src/crypt.c
index dfbf02c..5996070 100644
--- a/src/crypt.c
+++ b/src/crypt.c
@@ -162,7 +162,7 @@
 
     i = (int)STRLEN(crypt_magic_head);
     if (len >= i && memcmp(ptr, crypt_magic_head, i) == 0)
-	EMSG(_("E821: File is encrypted with unknown method"));
+	emsg(_("E821: File is encrypted with unknown method"));
 
     return -1;
 }