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/if_mzsch.c b/src/if_mzsch.c
index ddd3852..503a1e4 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -672,14 +672,14 @@
     if (!hMzGC)
     {
 	if (verbose)
-	    EMSG2(_(e_loadlib), gc_dll);
+	    semsg(_(e_loadlib), gc_dll);
 	return FAIL;
     }
 
     if (!hMzSch)
     {
 	if (verbose)
-	    EMSG2(_(e_loadlib), sch_dll);
+	    semsg(_(e_loadlib), sch_dll);
 	return FAIL;
     }
 
@@ -693,7 +693,7 @@
 	    FreeLibrary(hMzGC);
 	    hMzGC = 0;
 	    if (verbose)
-		EMSG2(_(e_loadfunc), thunk->name);
+		semsg(_(e_loadfunc), thunk->name);
 	    return FAIL;
 	}
     }
@@ -707,7 +707,7 @@
 	    FreeLibrary(hMzGC);
 	    hMzGC = 0;
 	    if (verbose)
-		EMSG2(_(e_loadfunc), thunk->name);
+		semsg(_(e_loadfunc), thunk->name);
 	    return FAIL;
 	}
     }
@@ -1260,13 +1260,13 @@
 #ifdef DYNAMIC_MZSCHEME
 	if (disabled || !mzscheme_enabled(TRUE))
 	{
-	    EMSG(_("E815: Sorry, this command is disabled, the MzScheme libraries could not be loaded."));
+	    emsg(_("E815: Sorry, this command is disabled, the MzScheme libraries could not be loaded."));
 	    return -1;
 	}
 #endif
 	if (load_base_module_failed || startup_mzscheme())
 	{
-	    EMSG(_("E895: Sorry, this command is disabled, the MzScheme's racket/base module could not be loaded."));
+	    emsg(_("E895: Sorry, this command is disabled, the MzScheme's racket/base module could not be loaded."));
 	    return -1;
 	}
 	initialized = TRUE;
@@ -1572,7 +1572,7 @@
     {
 	*p = '\0';
 	if (error)
-	    EMSG(prev);
+	    emsg(prev);
 	else
 	    MSG(prev);
 	prev = p + 1;
@@ -1580,7 +1580,7 @@
     }
 
     if (error)
-	EMSG(prev);
+	emsg(prev);
     else
 	MSG(prev);
 }