patch 9.0.1576: users may not know what to do with an internal error

Problem:    Users may not know what to do with an internal error.
Solution:   Add a translated message with instructions.
diff --git a/src/evalvars.c b/src/evalvars.c
index b0df0a5..bebee2a 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -206,7 +206,7 @@
 	p = &vimvars[i];
 	if (STRLEN(p->vv_name) > DICTITEM16_KEY_LEN)
 	{
-	    iemsg("INTERNAL: name too long, increase size of dictitem16_T");
+	    iemsg("Name too long, increase size of dictitem16_T");
 	    getout(1);
 	}
 	STRCPY(p->vv_di.di_key, p->vv_name);