Centralize catgets() calls through MsgCat

CDE has relied upon catgets() implementations following a relaxed
interpretation of the XPG internationalization standard that ignored
-1, the standard error value returned by catopen, as the catalog
argument. However, this same behavior causes segmentation faults with
the musl C library.

This patch:

- Centralizes (with the exception of ToolTalk) all calls to catopen(),
  catgets(), and catclose() through MsgCat within the DtSvc library.
- Prevents calls to catgets() and catclose() that rely upon
  undefined behavior.
- Eliminates a number of bespoke catgets() wrappers, including multiple
  redundant caching implementations designed to work around a design
  peculiarity in HP/UX.
- Eases building CDE without XPG internationalization support by providing
  the appropriate macros.

cde/programs/dtmail/include/utils/NLS.hh

@@ -1,53 +0,0 @@
-/*
- * CDE - Common Desktop Environment
- *
- * Copyright (c) 1993-2012, The Open Group. All rights reserved.
- *
- * These libraries and programs are free software; you can
- * redistribute them and/or modify them under the terms of the GNU
- * Lesser General Public License as published by the Free Software
- * Foundation; either version 2 of the License, or (at your option)
- * any later version.
- *
- * These libraries and programs are distributed in the hope that
- * they will be useful, but WITHOUT ANY WARRANTY; without even the
- * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
- * PURPOSE. See the GNU Lesser General Public License for more
- * details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with these libraries and programs; if not, write
- * to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
- * Floor, Boston, MA 02110-1301 USA
- */
-// $XConsortium: NLS.hh /main/2 1996/05/09 20:05:27 drk $
-/*
- *+SNOTICE
- *
- *	RESTRICTED CONFIDENTIAL INFORMATION:
- *	
- *	The information in this document is subject to special
- *	restrictions in a confidential disclosure agreement bertween
- *	HP, IBM, Sun, USL, SCO and Univel.  Do not distribute this
- *	document outside HP, IBM, Sun, USL, SCO, or Univel wihtout
- *	Sun's specific written approval.  This documment and all copies
- *	and derivative works thereof must be returned or destroyed at
- *	Sun's request.
- *
- *	Copyright 1993 Sun Microsystems, Inc.  All rights reserved.
- *
- *+ENOTICE
- */
-
-#ifndef _NLS_HH
-#define _NLS_HH
-
-char *catgets_cache2(nl_catd catd, int set, int num, char *dflt);
-
-#ifdef hpV4
-#  define GETMSG(catd, set_num, msg_num, def_str) catgets_cache2(catd, set_num, msg_num, def_str)
-#else
-#  define GETMSG(catd, set_num, msg_num, def_str) catgets(catd, set_num, msg_num, def_str)
-#endif
-
-#endif