patch 8.2.3069: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move some error messages to errors.h.  Use clearer names.
diff --git a/src/spellfile.c b/src/spellfile.c
index 264264c..058558e 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -5972,12 +5972,12 @@
 	// time.
 	if (!over_write && mch_stat((char *)wfname, &st) >= 0)
 	{
-	    emsg(_(e_exists));
+	    emsg(_(e_file_exists));
 	    goto theend;
 	}
 	if (mch_isdir(wfname))
 	{
-	    semsg(_(e_isadir2), wfname);
+	    semsg(_(e_src_is_directory), wfname);
 	    goto theend;
 	}