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/dtpdmd/Imakefile

@@ -34,13 +34,12 @@ SRCS = 	dispatch.c	dtpdmd.c	mailbox.c \
 
 OBJS = 	dispatch.o	dtpdmd.o	mailbox.o \
 	manager.o	records.o	setup.o \
-	util.o		nlmsg.o
+	util.o		nlmsg.o \
+	$(CDELIBSRC)/DtSvc/DtUtil2/MsgCat.o
 
 #if defined(LinuxArchitecture) || defined(BSDArchitecture)
 /* On Linux, just use the system provided Xau */
 DEPXAUTHLIB =
 #endif
 
-
 ComplexProgramTarget(dtpdmd)
-