Remove maintainer-check target, fold into normal build

make maintainer-check was obscure and rarely called in practice, and
many breakages were missed.  Fold everything that make maintainer-check
used to do into the normal build.  Specifically:

- Call duplicate_oids when genbki.pl is called.

- Check for tabs in SGML files when the documentation is built.

- Run msgfmt with the -c option during the regular build.  Add an
  additional configure check to see whether we are using the GNU
  version.  (make maintainer-check probably used to fail with non-GNU
  msgfmt.)

Keep maintainer-check as around as phony target for the time being in
case anyone is calling it.  But it won't do anything anymore.

doc/Makefile

@@ -12,5 +12,5 @@ subdir = doc
 top_builddir = ..
 include $(top_builddir)/src/Makefile.global
 
-all distprep html man install installdirs uninstall clean distclean maintainer-clean maintainer-check:
+all distprep html man install installdirs uninstall clean distclean maintainer-clean:
 	$(MAKE) -C src $@

doc/src/Makefile

@@ -4,5 +4,5 @@ subdir = doc/src
 top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
 
-all distprep html man install installdirs uninstall clean distclean maintainer-clean maintainer-check:
+all distprep html man install installdirs uninstall clean distclean maintainer-clean:
 	$(MAKE) -C sgml $@

doc/src/sgml/Makefile

@@ -22,9 +22,9 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 
-all: html man
+all: check-tabs html man
 
-distprep: html distprep-man
+distprep: check-tabs html distprep-man
 
 
 ifndef JADE
@@ -301,7 +301,7 @@ MAKEINFO = makeinfo
 ##
 
 # Quick syntax check without style processing
-check maintainer-check: postgres.sgml $(ALMOSTALLSGML) check-tabs
+check: postgres.sgml $(ALMOSTALLSGML) check-tabs
 	$(NSGMLS) $(SPFLAGS) $(SGMLINCLUDE) -s $<